I was going to look into changing my tpi set-up to the MAP (from MAF)sensor but I was woundering if you are able just to swap throttle bodies or if the whole plenum needs to change???

 

Judging by the way your question was phrased, I would do some homework before doing this swap.

http://www.eecis.udel.edu/~davis/z28/ecm_swap_730/

 

If you don't find the info you need on the Davis site (above post), then do a bunch of searches. There's more than enough info about doing the swap that you'll never really have a question that you can't find.
I just finished my SD swap.
But anyway, short answer, no, nothing really changes, a little bit of vacuum line, a new sensor, a jumpered knock filter connector, and maybe a missing MAF are all that will change under the hood.