Chevy converted to the one-piece rear main seal around 1986 and center bolt valve covers a year later.
Good start as hopefully your 350 likely has a one piece rear main and roller lifters.
If your choice was the CL110225-12 not the CL110225-1? it has a 208 Intake Duration at 050 inch Lift. I consider that a good cam for your goals. I always pick a cam and then go one below.
This procedure has worked excellent for me over the years.
https://www.summitracing.com/newsand...ion-calculator
Use this link for calculation the compression.
I get some thing closer to 10.5:1.
The aluminum heads will allow a higher compression without detonation.
I am missing details like the piston dish and head gasket thickness so it's just a guess.
The 3:73 are the real game changer. Most tend to underestimate the affects of a lower gear ratio.
Personally I would complete the gear change before anything else.
I can't remember for sure but the gear change may require a carrier change.
If you have to change the carrier do a posi if you can.