Are you saying that you do not yet have a car, but are looking at purchasing a 73 Duster?
That would be a good thing because they have enough rear wheel housing to receive reasonable-sized rubber, for their short wheelbase. Cuz without rubber, 300hp is already overkill.
Strictly a cruiser sorta means gears around 2.94/3.23 and 275/60-15s at 28" tall for low-rpm hiway cruising.... in lock-up, and that points to
a hi-torque engine.
With the LU convertor, you have two options of gears;
1) 2.45-1.45-1.00 running 3.23s your starter is 7.91, and 65=2520
2) 2.74-1.54-1.00 running 2.94s your starter is 8.06, and 65=2290
Without LU add about 4 to 5% so 100/250 rpm; 200 is typical.
These cruise rpms are high enough to run almost any cam and still get reasonable fuel mileage. But, I have found that a lot of this fuel economy depends on a couple of things, namely; CCP (Cranking Cylinder Pressure), and the length of the Power extraction cycle, and your engine may ask for massive ignition cruise-timing.
So then, it sorta behooves you to aim high on the CCP, and Long on power extraction; or some combo of the two.
Now, going back to the Hi-torque engine, Lots of CCP is again the target. We can get that in about three ways; 1) design, 2) a short period hydraulic cam, 3) a shorter period solid lifter cam. Short period cams have little to no idle lope.
Put that on hold for a bit.
With tall tires and tall gears, and a starter-gear of say 8.0 we have a bit of a problem. Namely, your roadspeed is 10.4mph per 1000 rpm plus compensation for convertor slip. Lets fix the slip at a straight-up 10%; so then; 2500 is 23 mph, 3500 is 33mph, 4500 is 42 mph, 5500 is 52 mph, 6500 is 61mph; you see where this is going right. As for Performance, and a city car, for practical purposes; you have a ONE-GEAR car. To make something of it, will take some fancy engineering.
But;
you said strictly a cruiser, and you're ok with as low as 5mpg, and it's a budget build.
So then, none of this matters; slap it together with a 318 cam and call it good.
But, if yur like me, you still want to spin tires occasionally; am I right?
Well then, the 28s gotta go or the gears gotta go, or the engine will need some serious CCP. Or you just up the stall.
Upping the stall is the easiest and fastest way to get tirespin off the line. And with a LU convertor, it makes the most sense. It will Not affect your fuel economy. If you go this route, say a 2800 to 3200, you can sacrifice a lot of CCP, meaning you can up-cam a fair bit, cuz that CCP was mainly making low-rpm torque/power, to help get moving with the very modest ~8/1 starter gear. By 2800/3200 that CCP is no longer a major player in torque-production.
Now then, you have a choice; Move the power up to a higher rpm , which will suck gas around town, or increase hi-rpm breathing in a different way and keep the cam modest.
With KB167s, the piston will fall in at around .012 below un-machined decks. You can run the .039 Fell-Pros and closed-chamber heads but the Quench is starting to get baggy (.051). Some guys, have successfully run .028 gaskets for a Q of .040, about middle of the road. But if you run open-chamber iron heads (budget) then it won't matter. So now your total chamber size is climbing to
2.5 deck +5 in the eyebrows, + 8.6 in the gasket, +72 in the heads, totals ~88cc, for a Compression Ratio of ~9.5
So at 9.5Scr with iron heads and no quench, to run on say 91 gas at WOT, will allow a maximum CCP/cylinder pressure of ...... say 155psi. At a mean elevation of 800ft in Missouri this allows a MINIMUM Ica (Intake closing Angle) of ~60* Badaboom.
Since it's a One-Gear car, we can run any LSA we want, so lets tighten it up to 110*, to get a lil power in the midrange, but still be able to rev it out a bit. And I get a hydro of something like;
262/270/110, which has 119* of compression, 115* of extraction, and 46* of overlap, with the specified Ica of 61* when installed straight up at 110*..
As for that 115* of extraction, this, together with; the 155psi CCP, and a cruise rpm of 2290, points to fairly thrifty fuel useage at steady state cruising. And not too bad around town if yur taking it easy. IMO; this is the smallest cam to run with 9.5Scr and 155ps, with iron open-chamber heads and no quench. If it was me, I would just do a simple valve job and call it done because this 262 cam has a fairly modest powerpeak of around 4800/ maybe 5000 installed "straight up".
As for the 46* overlap, this will idle like a 340.
As for the 270* of exhaust duration, this allows you to run cast-iron manifolds.
As for the 262* intake duration, this will allow you to run any old dualplain intake or very small-runner/small plenum single-plain.
Very budget friendly.
One of your biggest expenses would be the hi-stall LU convertor. To that end, I would just install the complete A999, as found with it's factory LU, and try it, You may find it to be reasonably satisfactory, with the 3.23s... even more budget friendly.
The point id this;
you said strictly a cruiser, and you're ok with as low as 5mpg, and it's a budget build. This is practically a bolt-together engine with the only expense being the tall pistons.
For the ultimate in cheapness, you could run the stock 360 2bbl cam (252/260/112) with an Ica of 56* when installed at 110, but the CCP rises to about 161psi, so you might have to run 91gas at WOT; you can still cruise on lesser gas. With the extra pressure, you can run any old A904 with any old TC, but with the 3.23s, and for cruising 65=2620 @4* slip with the 28s. Can you get any more budget friendly than that?
At this point, I gotta say something else.
This car will really like a lil more gear; 3.55s will get you close to 3500 at 30 mph on the kickdown into First gear and 65=2850