525 EFI whipple kit "tweaks"
 

I am installing these this fall and since they've been out for a while I assumed there would be lots of info on going to 900 Torq. It seems odd that my 502 MPI with a much smaller side mount whipple will make 800 and that engine was only 425HP to start... Engines have less than 100 hours of run time over 1200 rpm so I don't want to change pistons yet... A cam swap? Heads will be off for studs and gaskets so possible port work?

your 502mpi with a side mount doesnt make 800hp unless the rest of the engine was heavily modified.
3.8L 525 runs right around 800hp on my dyno.
if you modify the engines, you'll need to modify the 555ecm fuel map. thats something only a handful of guys in the world can do, and unless youre following a recipe theyll be taking guesses remotely and thats a bad plan.
If your engine is the old 502 mag side mount deal and its relatively stock, i promise you a 3.3 or 3.8 525 engine will blow it out of the water.

As Saris said no way a side mount on a 502 mpi will make that kind of power, what are you going to use for the EFI control

What size pulley did you run on your side mount to see 800, whos dyno? John lambregske (polebarn racing engines) brought a 522 to my shop that had a 2.3 sidemount, solid roller, iron heads that had about 5 lbs of metal taken out of them, mpi intake with all the mods, , you get the picture. With a 2.7 " or whatever smallest pulley they made for it we did see a touch over 800 ft lbs and just shy of 800 hp (in dyno trim and open headers). His IATS were UN-SUSTAINABLE because innercooler is just too small, but hes damn near 80 years old and says he just wants to blip it for short burst.
So when you say "525" whipple kits, are you talking real 525s w the 555 pcm? If so, keep in mind someones got to be able to tune it and theres very few choices there, everytime someone calls and ask me to dyno or tune a 555 ( which I CANNOT tune), I tell them to consult with Mark boos or whipple BEFORE proceeding with their build to make sure they can get a tune for it