Renegade is one of the best in Porsche V-8 swaps. Another good source is Kennedy Engineering, they have been doing 914 & 911 adapter systems for more than 20 years.
When considering this for the Fiero however, you need to remember a couple of things. On the 911 kit the engine hangs out back of the transaxle putting most of the weight behind the rear axle CLine. If you are going to try that, why not use the the 500 HP Prosche engine too?
On the 914 swap the engine is in front of the rear axle CLine (Mid-Engine). However, to use that setup on a Fiero you will have to stretch the wheelbase about 12". You see the length of the engine and the length of the transaxle that is in front of the rear axle CLine means that the engine will come into the passenger compartment by about 12" or more.
Besides, have you checked the prices on one of these Porsche transaxles?
Hope this helps
Archie