Anyone know the "rules" about the 305 block (single rear main seal/roller lifters and/or two piece seal/reg. lifters) boring and stroking.

First question: How are "305" and "350" related? Do all heads swap? Are the block similar enough?
Puting the 350 crank and rods into the 305..is this possible? If this can be done are the maching costs more than a used 350 block? Has anyone done this?

For the poor folks that need the original 305 block number...what can we do...how far can we go with regards to max cubic inches vs. costs vs. dependability.

 

The 305 and 350 are identical in every way, except the 305 has a smaller bore. The crank and rods in your 305 are the same parts GM used in the 350.

Don't bother stroking a 305. It has enough breathing problems as-is with its tiny little bore. Stroking will only make things worse.

 

The rules are, it doesn't make sense; because a 350 block costs about $50, and that's cheaper than anything you can do to a 305, and makes more difference. Cheapest power money can buy.

The 305 and 350 have the same stroke; the same crank forging in most cases, in fact. Balanced slightly differently, but the same raw forging machined to the same dimensions.

The only difference is the bore. The 350 stock bore is 4.000"; the 305's is 3.736". A little over ¼" difference. You can bore a 305 byabout a tenth of that, safely; and maybe get lucky and bore it by one-fifth of that, if the block happens to have come out unusually close in tolerance. So it's not anywhere near possible to turn a 305 block intp a 350 block. No one has ever done it, in a practical sense. It's theoretically possible to drill the 305 cyl walls out and put 4" sleeves in it; but the cost would be far in excess of just picking up a 4" block from buzzard.

Heads are the same, except for chamber size. Also, 305s usually have smaller valves, since there's less motor to feed; and also, larger valves come so close to the bore that they do no good, because no air can get between the edge of the valve and the bore. You can actually make heads flow less on a 305, by putting larger valves in them. It's even possible for the valves to extend outside the bore, such that they hit the top of the block when they try to open.

There are cranks and pistons made for increasing the stroke to 3.75" in a 305 block, which gives a 334 (if also bored .030"). It's only sensible to do that if the numbers-matching thing is REALLY REALLY important, which it virtually never is.... I can think of no organized racing class that requires it, and if you're wanting to keep the car "original", either get another engine and put the original motor in storage and don't hot-rod it; or don't hot-rod it at all.