318 Build suggestions

3.91 plus .040= 3.95

At street power levels, the bore size difference from 318(3.91) to 360(4.00) =.090=2.3% means very little. The same cannot be said for the stroke difference; 3.315 versus 3.58 =.265=8%

The thing about a streeter, is it's a two-gear deal. No sane streeter is gonna be topping out third gear on a regular basis if he wants to keep his license and or car. So you might as well gear it to top out in second at around 65/75 mph, and make sure your brakes can scrub off speed in a hurry. So build for build, the 360 can hit more bases with fewer dollars spent.
the bases are;
rpm to the top of second gear
rpm at kickdown into first at say 32 mph
cruising rpm @ say 65mph. If you cannot cruise your streeter comfortably for a couple of hundred miles, then you really don't have a streeter. I don't care what anybody says, my car cruises at 65=2240, and I have cruised two days one way with no fatigue.
Ok so, choosing that comfortableness is a highly personal matter, but typically, I would say, that is, IMO, 2200 is comfortable, and 3000 is not. So the median is about 2600. For me, that is still too high, but everyone has an opinion.
Now, to cruise 65=2600 with 27" tires will require about a 3.23 gear. These will get you 65=2640 at zero-slip/ say 2750 at 4% slip, on the tach.
So that sets the stage for everything else.
the following is for an automatic equipped,3600pounder , all loaded up; With 3.23s,
cruising at 32 mph is then 1880 in Second gear, and at KD will be 3180 at zero-slip/ perhaps 3500 on the tach.
And top of Second will be 60=5240@zero-slip/perhaps 5770 on the tach.
So from that, we know the power-band has to be from 3500 to 5770 =2270.
Next; 300hp is a nice street power level, I wouldn't build for any less. And by 380hp, most of it is going to tirespin, so unless your plans include serious traction improvements, IMO, 380 is overkill. So then a happy median is 340hp.
A 360 will do that with ease; all stock internals, stock iron heads even, and maybe a 224 to 230 cam @155/160psi cranking pressure.
What's the 318 gonna take?
Well by the time you are done, the only things still 318 will be the crank,the block, and maybe the rods........ cuz you will have 340-ized the entire top end. So is it still a 318? Yeah sure like milk is ice cream.
I don't get it.

Back in about 1968, Ma put the 440-4bbl top end on a 383 with a 440 cam and thus was born the 383Magnum, so I guess this 340-ized 318 could be called a 318Magnum.
Oh but you love your 318, but for some unfathomable reason, you rail on the 360 which is just a stroked 340. Everybody loves a stroker...... unless it has a 3.58 stroke; somehow that is unacceptable.
I don't get it

Back in the early 2000s, when my car was fresh, I used to take it to carshows and drive-in meets, and such. And I would get an earful of "oh you shouldda built a 340; those were fast"........
Now, my 360 is a 4.04 x3.58= 367, so I switched to calling it a stroked-340, and that was the end of poo-pooing the 360. Now it was all "oohs and aahs".
I don't get it.

I have had several 340s some of which I still have and use as doorstops, cuz the 340 is "just a bored out 318/ destroked 360/ a tweener."
The 318 is and forever will be; "the little engine that thinks it can." It can hit each of the bases with a specific build, but it can never hit them all, nearly as well as a 360 can, in a 3600pounder.
The average power from 3500 to 5770 will never be, build for build,comparing apples to apples, as high as the 360. And the 360 will cost waaay less to make it happen. With KB107s and 63cc chambers, it falls together at over 10.5/1 Scr, all ready for that 230/110 cam; almost tight-Q and all. Just bore it, stuff it, and screw it together, & d-o-n-e.

But yakno,
from a 360 to a 408 is plus 13.33%; oou, everybody loves a stroker.
from a 383 to a 440 is plus 14.88%; oou, everybody loves a stroker.
from a 318 to a 360 is plus 13.21%; Alex, I'll take 318 for the; oou, I like my 318 factor, cuz it will do everything the 360 cannot do, Alex;
says the Ostrich with his head in the sand.......
I don't get it.
A streeter is not a drag racer. You might be able to build a competition 318 with unlimited rpm..... But that ain't a streeter, married to a specific streetable rear gear.
Oh sure put some 3.91s on it and you can have fun. But how far can you cruise at 65=3400/3500
Oh sure you might be able to squeeze out say 20mpgs with 2.76s, and a small enough cam to stay out of reversion,...... but you'll need to supercharge it to get that up to 340 hp.
I don't get it.

Don't even get me started on
if you have a 4-speed........build for build and gear for gear; your teener is out classed on every front, hanging on with desperation.