Help Rebuild 350

The motor has been taken apart because I though it was frozen. After getting down to the block, removing the out drive did the trick. The out drive was frozen. I bought this boat without the engine starting because of this. So I assume that everything is ok. But I'd rather clean things up and upgrade for 300hp and possibly EFI It will be pushing a 1983 Wellcraft Aft Cabin 230.

There serial numbers are not visible on this motor. The tag is rusted and unidentifiable. The only readable numbers are:

BLOCK CASTING ID: 10066036 (350, 2 or 4 main, hecho en mexico)
Head ID: 98417369 (GM11, hecho en mexico)
Intake ID: 246250 10
Carb ID: Rochester Quadra Jet 1980 california model

As far as I know, it's original. How can I figure the current/future HP/torque? What are some resources that may help me figure this out? (Software, Books, Websites)

This is a project and a learning oppertunity. I'm a newbie at rebuilding but with some guide, it will be fun.

Thanks!!!