A 3.810" bore would be a 256 engine or a 270, bored .030" oversize. I believe you said the pistons had "30" on top? A 256 has the same stroke as a 248. Rod and main bearings will be the same as the 248. A 270 also has a 3.781 standard bore, with a 4" stroke. You MIGHT have a 270 that has been bored 30 over and re-stamped with the original engine number. Check and post the casting/forging number on the crankshaft, please. I have a list of crank numbers to reference.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!