So while the trans is out the next couple of weeks... I 'might as well' install the new Pypes exhaust I bought last summer which means I 'might as well' either paint or undercoat the underside of the floor pans since I will have everything out of the way and the car up high enough to get to the bottom side.

The floor pans were replaced recently with new sheet metal.  The only coating on the underside is the edm protective coating.

Should I use some spray on or roll on undercoating to minimize heat and noise, or just rattle can some rustoleum on to add another layer of protection?

I've heard pros and cons of both ways.

Other than some degreasing and scuffing, that's all the prep I should need to do.

Let me know what you think.

Don't know about the underside treatment, but let me know when you're doing the exhaust... I'll clue you in on some tips/tricks I learned when doing mine (and I've got some 2-1/2" stainless bends that may be helpful).

I think that EDM stuff is (supposed to be) acting as the primer. If it were me, I would scuff and spray on something like a 1K etching primer, then paint it with whatever underbelly paint you want like Eastwood. GM used to sell restoration paint by the gallon, but it was made by someone else. Car Quest has a paint and auto body division now and many body shops (including dealers) use thier products. Lowells is another source. Up north by me, Welle is a good place to go too For dound deadener, I prefer to have it inside. Undercoating is a nice coverup, but a pain to take off if you have to. Body Schutz is a brand that I know several places use if they have a beater car that gets a quick floor patch and needs a cover up.

If they look good, paint them... if they look terrible, and you want to hide it, use undercoat.

Eastwood chassis black satin is on the way.  Going with the paint option since the floors are in such good shape.