If you go with the Boss turbo you have many to chose from. In a stage 4 there is a 50 trim@450hp, 54 trim@475hp, 57 trim@525hp in the E cover. In the stage 41/2 you have 50 trim@425hp, 54 trim@475hp, 61trim@525hp and the stage 5 with a 54 trim@500hp.
If you are going to street race go with the stage 4, if you want to use it more on the track use the stage 5, and if you want both go with the 41/2 stage.
You can also add the BB at a small extra,well worth the extra. I should also point out that the hp numbers are at the crank and is not at the rear wheels so maybe you need to look a little bit larger hp.
Greg