Got some gt40ps And intake

well just polishing will help quite a bit. it will increase flow of fuel and air because the surface will be much smoother and less restricting than the cast surface. and more air and fuel = more horsepower

I've played around a good bit with those old OEM iron heads

Here is a thing or two to keep in mind about em

KNOW ... what you can expect
or
What you can't except out of em

TMoss and Thumper have realistic info about em on their sites

Smoothing and polishing is not gonna do all that much

Matter of fact ... Ya DON'T want to polish up i ports TOO much
as it can cause the fuel to puddle

Just a basic tid bit of info is this

The e ports of ALL OEM iron heads just SUCK

That is where most of your focus needs to be made
but
It will take more than sanding rolls and a Mickey Mouse Dremel

That being said ... I'll leave you with what I feel is most important :Word:

If you are not careful

By the time you buy
compressor
die grinder
porting burs
valve job
valve springs
and all the rest

You can easily have dumpped close to the amount of money you would
have in a nice set of much better flowing Aluminum heads

You used to be able to get some good info from the Standard Abrasives
site but I don't know if it is still around

You do have to do your research to know what
or more importantly
What NOT to do

Or you can grind too much and poke through a water jacket
and
You can remove material from some places which is a No No

Bottom Line Is

Yes ... You can improve their performance
but
Only you could say if its worth it

Don't expect too much or sink too much cash in em

Grady

Did you look at the info provided by Thumper and TMoss

Did you look at the Standard Abrasives site

Grady