225 slant rebuild for more power

Welcome to the club.
I completely rebuilt the 225 in my 64 Val because it was locked up when I got it. Following recommendations here I did the following:

Milled head 0.080 but you should consider going 0.100. As Charlie says, no downside, big upside. Modern head gaskets are at least 2X thicker than the original steel shim gasket so you'll lose a little compression. I did a complete rebuild so had my machinist install hardened exhaust seats with valve job. I did a little pocket porting and gasket match because it was only my labor, free!

Block bored .040 over with Silv-o-lite pistons and moly rings.

Sent the cam to Oregon Cam grinders to be reground. Talked to the owner and he recommended 2 grinds and I went with the milder because it's a driver. I'd say it's between 318 and 340 specs.

Did a little porting on the stock exhaust manifold and gasket matched, free labor.

Rebuilt the stock BBS carb. Advance timing to 10* BTDC.

Anyway, it drives great. Never feel a need for more when driving. Best ET was 18.4 secs. Got almost 24 MPG going to Carlisle. Have about 8000 miles on it and haven't touched it.

You can do less and be fine. Since you are taking classes, disassemble completely, new timing chain, maybe hone and re-ring, check bearings, oil pump, etc. and inspect everything. Dyno proven that biggest increase in power is going to 2 barrel carb.

You need to read this section and check out slantsix.org
Disregard the haters who say V-8.