There's every possibility the block was originally a 283 and it was taken out to 4" and has a SJ 327 crank fitted. Building a "301" SBC was the thing to do before 4" bore blocks and factory cranks larger than 3" stroke became a dime a dozen (late '60s, early '70s). The success rate for getting clean (no inclusions) 4" bores out of a 283 wasn't great- but it was good enough that it was done tens of thousands of times through the years.
For s&g, look to see if there's still a suffix code on the passenger front of the block. If the block was milled it will be missing but if it's there, it'll tell you what the original application was. The date code might also be used along w/the other info to help pin it down.