I voted 318... if you disguise it as a 273 commando...
Don't bother with the different/ later rods, it doesn't matter for what you're doing and the early 318 forged crank/ rods are more than adequate and the same as 273 stuff. Keep the crank and rod sets paired and be sure to number the cap and rod for reassembly. If you can, put the rod cap nuts back on until you are ready to install bearings.
You don't need to balance anything, unless you really want to. The KB pistons, as well as any other oversize or standard replacement cast pistons are going to be within factory balance tolerances, on the light end. You will get more out of the engine on the high RPM end if you are going to balance, in TQ/HP numbers, but it really doesn't matter for a street engine. It will hit 5k no problem and run smooth. Remember, the light/ small end of the reciprocating mass is only considered at 50% of it's actual weight for balancing, so even with slight differences, if there are any, make less of an impact on crank balance. The big thing is to make sure you keep track of the rods that go with the crank and put them back in order, for the big end.
If it's in your budget, you might balance and resize rods with new bolts, but it's not a deal breaker if you skip it, as long as you use a beam wrench to put it back together, like I didn't the first time and had a cap come loose, due to a faulty wrench that read 13-14lbs high. haha...
The 318 with KBs will give you a 9.68:1 if the 302s have open faced valves and cc check around at 62 like mine did. You might drop 1-2cc with flat valves. If you do, it will be closer to 9.8:1
Those pistons hit at .011" from deck, so with Mr.Gasket 1121G .028" gaskets, you wind up with a good .039" quench. No need to zero deck unless you want more compression. Those KBs will get you there without any cutting, if everything is square, but make sure that everything is, or better yet, your machinist, because those 1121Gs need it to seal. I went through a set with a coolant leak on assembly with one head that needed .007" cut and went .010" on my heads. I ended up with 61.5cc, so I radiused the sharp edges on the heart chamber to get it back up to 62. It kept the stock length pushrods just fine on cam centerline and helped a bit with total lift loss from pushrod angle that LAs have, but I did it for the straight surface and nothing more. I didn't have the intake sides done and had no problems fitting the intake.
I paid $380? for the KBs and they did it the right way. If you go with the Sealed Power, you will need to shave a bit from the block to get good quench. Never mind shaving the heads, as that won't bring the piston any closer to them for good quench and they have good CC as is.
If you do take anything off of the heads, just clean them up if they aren't square.
I'm running the same intake and I think it's a great combo for the street with the high velocity heads. Very throttle responsive, but well mannered on the street. Just be sure to pull the pegs from the front and rear of the block at the intake manifold front/ rear and center the manifold, and adjust the bolt holes as necessary. I had to rat tail file a few on my LD4B to get it to sit perfectly centered on my engine/ heads. You don't want the pegs indexing anything, so don't drill the intake. Just pull them and leave them out, use RTV and no gasket, front and rear.
If you gasket match, be sure not to use a 340/360 intake gasket and don't use a cork front/ rear gasket. They crack aluminum manifolds when tightened. The FelPro 1805 set is your magic number. Comes with cork front/ rear that you don't use and the correct 273/318 port size for gasket matching.
