The question of would it be legal has turned into should it be legal, and i will offer my 2 cents, after all, it's as worthless as anyone's.
If a person is allowed to build a 400 cubic inch engine from an 88 block, and run it in the stock class, then why can't a person install a 310 engine and run it in the stock class? The 310 engine swap would be more affordable for the average person.
Same goes for any engine swaps for farmall/Oliver/mini/Massey/Ford/etc.
Unless you are prepared to test for displacement, compression, and horse power, then having a stock block rule only benefits those with the money to modify their stock block to higher power levels.
It may not be perfect, but speed limits seem to be the accepted standard of controlling power.
If we all can admit that their is no power limit in the rules, and we don't want one, then why not allow any bolt in block?
If a club wants a power limit, a dyno is the only way. Having a stock block rule will not limit horse power, but having a horse power limit will keep out bigger blocks.
If the rule says no 310/320 block, then that's the rule. However, if the intent of the rule is to limit power, then it is kind of pointless. There are many ways around that. If the intent of the rule is to only allow big power to those who have money, then the rule should be re-examined.
That's my 2 cents. Hope you got your money's worth.