jackson

Between cup's big block & sb2 eras ...
... 4 1/8 (old sbc 400 block) x 3 1/4 (327 crank) was basis for old cup motors.
Approximately same BxS dimensions remain ubiquitous in cup etc.
FYI ... a thin sixty over 4.185 400 block with a 3.48 350 crank also makes a 383. Most 383 are thirty over 4.030 350 block w/ aftermarket 3 3/4 crank. Some 327 blocks are not exactly like a 350 ... & may have tougher clearancing issues if a 3 3/4 crank's attempted ... dad's may or may not be so hindered. Get a cheap 350 block if you're gonna build a 383 ... save the 327 for someone needing 327.

cardo0

I find its more fun to build a motor for as little $$$ as possible rather than spend big $$$ on a street driven motor.

Yes a 327" for free to rebuild would be a lot of fun and a great way for a first time builder to learn. Solid cams, cheap Eutectec pistons with lower c.r., rebuild and pocket port the 202 heads or at most buy cheap Vortec heads.
Biggest cost is the machine work. But for well under $2K u will have a hi reving engine that with c.r. < 9.5 can burn cheap regular gas and take a beating all day long.
BTW those early blocks will take 0.060" boring easy. And u already have a great forged crank to start with even with the small journal.

350 hp should be very easy. 400 hp wishful thinking but at least close to it for very little $$ out of your pocket.

Hope this helps ya' and let us know if u have any specific question.
cardo0