New 3100 top on old 3100 block

[3dg3]

I have a 99 Buick Century that I'm getting ready to do a LIM gasket repair on. While I'm in there, I was just going to do the head gasket too just for kicks, and do a port/polish and valve job
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I was reading that the 2000+ 3100 has better flow. What would need swapped over? I saw that to do a 3400 top swap, you'd need new pistons, custom pushrods, etc, and I don't want to get into that.

[young gun]

I believe it was just the upper intake manifold of the 00+ 3100's that flowed better. Someone will chime in if there is more to it

[Guest]

Both the upper and lower need to be swapped.

[caffeine]

For 3400 heads on a 3100 the same pistons and pushrods are used

[3dg3]

So if I was going to do a top swap, would I gain anything from swapping the heads too? I'm going to a pull yard Friday and will take off as much as would benefit, but I don't want to have to change pistons or things like that.
Would I be able to mate 3400 heads+intake manifolds to my 3100 block without much else?

[3dg3]

Just to clarify, the engine right now is an l82

[1QUICKHATCH]

To make it easy you will want to get a 96-99 3400 heads, lower intake and upper intake. If you do the 00+ 31/3400 you will have to swap out the egr valve or get an adapter. You will also want to use your injectors. The 3400 throttle body is also an upgrade over the 3100 TB.