3.8 head changes. help?

I bought a bunch of 3.8 stuff today. A block from 1991(?) and heads from 1996, along with two intakes (1992 and 1996) and a 1992 plunum.
I have an 89 tbird with the 3.8, and the valve springs and valves look different. The ones on the 96 head are cone shaped, and my 89's are straight. Im wondering if the newer heads will fit (and function) on an "older" block.
Anyone ever try this?

so far I have found that felpro uses the same headgasket on anything newer than 88. the intake valves are .08 inches bigger after 96. intake manifolds are smoother, but lack an IAC. and the intake bolts are a size smaller. hopefully it wil run. I shal call her frankenbird...lol

I meant IAT, not IAC. I got in finnished last night. seems too runn pretty well. now I'm getting a random check engine light. codes 51 and 91- system too lean, left and right sides.