FelPro, or Timken both manufacture rear main seals for the 2.8l. There are others but I would look at these first. I recently used the FelPro on our 2.8 and all is well after 1000 mi.. Install was easy. Clean shaft and block surfaces well and put a very thin coat of grease, or oil on both sides of the seal prior to pressing it in. Some use rtv sealant on the block side and oil on the shaft side. Additionally, you will find that the replacement seal types are allot smaller than the OEM one you took out. Really not that difficult of a job if your trans is out anyway. Fiero Store and Rock Auto, and many others, have the seal you want.
You probably should also do the cam shaft seal, just above the main, while your there, just cheap insurance against any leaks. For the cam seal I used a Victor seal, others available, with thin black rtv on both sides.
[This message has been edited by Kevin87FieroGT (edited 06-16-2014).]