Belcher,
I don't know what gains are to be had from this mod.
But The hp improvement stated by manufacturers is often not a peak HP figure. i.e. you might make 140 hp at 2000 rpm but with a part that makes 10 hp you could now make 150 hp at 2000 rpm. But still only make 260 peak hp.

I do however have experience with Accufab with my Mustang, and I think they are an excellent product, and the throttle response should feel much better.

SJR