i don't have a smallblock but I have a 4.3
in 86 the changed to roller lifters and a one piece rear main seal etc
in 96 they changed to the vortec heads so intake ports changed size, different manifold bolt locations and number of bolts.. etc... totally different setup you can put the 96 heads on a pre 96 block with the right intake I did that on my 4.3 with a 91 block and 97 heads with an edelbrock intake
header fitment is going to be difficult there are very few that will fit and clear, only ones I have heard of are the block hugger type and the oe rams horn type info about both can be found on the site if you search
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Luvless
1980 Mikado-Sold.
1993 Lexus SC400 my Daily
2004 Yamaha WR250F my new love in life
2016 Toyota Camry my girls ride