Short story long, Brutis (My 87 F-250) was originally equipped with a carbed 460 and C6 trans . I was never exactly thrilled with his performance and downright horrified by his gas mileage.
Recently, I replaced the old worn out engine with a more modern EFI unit complete with the fuel injection, F3TE heads, and remote mount TFI .
I kept the C6, (I used a computer from a 460 with a 5 speed to do this) but overhauled it and used the gear sets from an E40D .
Man what a huge difference in the truck !!!!
However the EFI 460's air reduction horns (those littly bitty things in the intake hoses) coupled with the rain/snow flap on the core support to airbox ducting were obvious restrictions . So I spent some time on them with a saw .
This made little difference in off the line acceleration . (In fact I couldn't notice any difference) But yesterday those modifications came in to play when I had to pass a Semi. Then they were very noticeable, making them worth the effort and something I would recommend.