My 91 has a WC T5 (Borg Warner)...

I picked up a Summit Catalog, says Tremec Transmissions, the very first couple of transmissions are T5's ... Then later you get to the TKO 500 and 600...

Are Borg Warner & Tremec related???

Also, why would you spend almost $2k on rebuilding a t5 with parts from a company that may only guarantee them for 6 months when the I saw some TKO 600's on Ebay for under $2k, shipping included & LIFETIME SERVICE WARRANTY???

I want to keep my some 5 speed, but will someday upgrade the motor / rear end / trans... gotta have something to handle the D1SC

Raf

because there is a sucker born evey minute

The tko's are beefy transmissions, just make sure you get one for a 3rd gen with the adapter plate. I think they have a longer input shaft.
Fortespartsconnection is the place to go.