How much would you charge

You'll need a header and free flowing exhaust plus a compression boost to make that of any significant value, So there goes another pile of cash. Then there's a TC involved, and probably gears in your future. Did he mention any of that. What's all that total up to? $2500?
And for what, 30/35hp?
Lessee 2500/30~$83 per horsepower.
Lessee what could I buy for $2500? I know, a junkyard Truck Magnum, with an overdrive 4 speed,a car oilpan, engine mount adapters, a used intake and 4bbl,plus new dual exhaust, and possibly a driveshaft. Oh heck you might as well take the Sure-grip 3.55s to 3.91s rear end too, while yur there.
Lessee 2500/145~$17 per horsepower.

My numbers might be off a tad, but you probably get the point.
Which is:
Make sure you get the WHOLE picture.