How much power do engine mods yield?

Ben Drinkin said
Done correctly, that group of mods, along with the rear end gears could make a night & day difference. Still wont set the world on fire, but it will definately be a lot more fun to drive.

Thats about it in a nutshell.

No need for dual exhaust on a slant. Just run a single 2.25-2.50 exhaust through a free flowing muffler.