Go with the 454. Ain't no substitute for cubic inches. For a cruiser it will be great. The KB201 pistons will work well on unlead premium.
I don't know what F-Bird 88's beef with ProComp BBC heads is. I've sold more than forty pairs of castings and they have all been top of the line. I like them better than several "Brand name" $$$$$ heads. For a common sense street/strip build they are the best.
Use just the ProComp oval port castings and then install Manley valves and good springs.
Up grading the iron heads can get expensive real fast. Guides and hard exhaust seats cost and then you still have to buy new valves, springs etc.