Forgive the Noob questions, but...
 

Looking at an 89 vert.

Did these have LSD, and if not, would an FB 4.011 lsd pumpkin fit?

Is the stock exhaust on the FC as much of a cork as the stock exhaust on the FB?

Thanks.

From the FAQ:

Did my 2nd Gen RX-7 come with a Limited Slip Differential?
Only the following USA model 2nd gen RX-7s had a LSD from the factory:
86-88 GXL
87-91 Turbo
88 GTU
89-90 GTUs (however not the 89-90 GTU)

That doesn't mean it's impossible for it to have one though. It's a pretty common swap. Look for a metal LSD tag on the filler hole on the pumpkin.