Well it's a little more clear of your goals now.
So lets look at a few things,
Since your pulling an engine to swap into another truck, now is the time to take care of stuff, not later.
You say you want more power for trailer and sled pulling ok that's doable with these trucks. How you go about it is whats key.
IMHO, or others may say Less than HO,
it's a short block rebuild to start!
Cam, either Typ4 from Russ here of the R&D cam, both are effective at more power, it's how and when that power cure takes place that is the difference.
Since your into pulling a cam, now is the time to STUD the heads, check around on prices, but since your studding heads, new HG too which means you get a LOOKSEE in the engine now! Well since your into it this far...drop the pan, inspect the bearings while at it right???
NO PAN GASKET EITHER, just a nice bead of RTV Permatex ultra copper or something good like that!
Ok so now we have the CORE looksee done
Heads, PORT n polish them and throw a valve job in while at it. of course the standard checks for flatness and such need be headed.
Ok so top end done, lets look at fuel,
There are a few options of which both are mentiond.
Mel at Conestoga Diesel makes a slightly better n stock Baby Moose, a good turbo cal pump MOOSE, and the illustrious SUPERMOOSE for some significant power increases.
R&D makes a decent pump too and then has their Hybrid DB4 setup for some wicked power too.
Any deceint turbo/pump/cam combo will indeed need the benefit of an Inter cooler to make use of the level of boost and fuel you'll run so you likely have to factor that in too!
Check with both, your call where you want to throw the $$$ too.
As for the Turbo, Russ again Typ4 makes some hot rod mods to the stocker that can help you out, or if your a fab freak you can do something entirely custom too!
As you can see there are options here that are all viable and can make good solid power up to 375 HP Dyno proven HP, speculation of 400HP is just that, an untested un proven level. Please don't get me wrong it's not that I don't think we can't attain it, I'm saying it's not done yet!
It is all in your court where and what you want to do.
Ceramic coat the pipes and parts etc
Anyway, that's what I gotta say on it thus far,
Let us know what yer thinking and perhaps we can help further.
Al