Manual trans? If 4L80E trans, I'd be tempted to spend the bucks and get a Holley terminator with the built in trans controller and GM trans harness adapter so you can control it all.
Pulling the heads? My 93 had rotators in every single valve spring, so replace those. I run comp 911 springs. Get new hardened pushrods. They also sell adapters to make the factory rockers adjustable, $100 or so but don't bottom them out if pushrods too short, it'll crack the sleeves.
Not sure about the 90, but on my 93 with the serpentine belt, the front of the manifold you'll have to clearance some metal to fit the factory Y looking bracket as well as deep tap the water jacket plug to fit the Y looking metal bracket on driver side front corner.
My 215/215 comp magnum hyd roller pulls to 5000 and barks the rears on the 1-2 shift in my Suburban.
Might just get a whole top end kit to upgrade the heads. More cam and peanuts is a losing proposition since better heads is always the best choice, but not cheap.
