Yup, you'll need one. I got mine from Steeda... And I have a BRAND NEW spacer, still in plastic for sale. I had 2 cars with Tremec's, and sold one with a stock T-5.. So I put the used one in my car, and have the brand new one for sale.. PM me if interested.
or you can just get an AODE driveshaft. bolts right up. I pulled my stock AODE shaft off my old stang and tossed in the basement when i swapped out to a T-5. bought this car that had a T-3550, had driveshaft problems, bolted up the old stock one from the basement. works great.
If you don't need the tranny right away I would try to wait for Astro performace has full stock of there "super t-5's" which are roughly 50 bucks cheaper then G-force trannys and just as strong. I was told by Astro by the end of Jan early Feb they will have full stcok of 94/95 super t-5s. Fiarly cheap at $1,895.00 for a t-5 that can hold 650hp/500tq with the "Upgraded" 9310 Alloy Output Shaft.