Am interested, too, in the 100mm intake.
Sounds as if you have a tubular exhaust manifold. If so, does it make much of a difference to power ?
My reading about plug-ins leads me to think they are not good.
More power for you = remove back exhaust box and go for propane fumigation. Can be significant bettering of acceleration and fuel consumption if used correctly. Can be significant engine damage if used incorrectly.