307 vs 350

[rx7speed]

ok I found this block at my moms house

it is a 307 block but the rear flange on it looks like the flange from a 350

what gives?

I don't think it would be worth it to put the 350 crank in there

any ideas as to what you guys think is going on here

[91 Formula 6.3L]

A 307 is a small bore 3.875" block from a 283, with a 3.25" stroke crank from a 327. I believe it uses 350 mains.