How hard would it be to rebuild my heads. I have a leaking valve seal and if I pull the heads off, I want to rebuild them. What all is involved? What tools and gaskets and other items will I need?

or is there somewhere that sells fully assembled heads??

Just a straight rebuild no performance modding?
New valves, springs, gaskets, valve locs, retainers, and a good clean job. Plus new push rods (cause they're cheap).

You could also take them to a machine shop and about $500 they can rebuild them for you.
Polish and porting with larger valves and a shaved deck can add up quick, Intense sells stage 3 for around $1800 but no need without an aggressive cam to match.

are there mods for the series I heads?

Not off the shelf, but a good shop can do anything you want, including larger valves.

Tsk Tsk willie...lest we forget the 1.72 roller rockers? hehe
They're not cheap though

Custom ones would probably run about the same, or modifying some Small Block Chevy ones to fit.

Did the chevy thing ever get proven? and err...who makes custom rockers?

The SBC ones were fully completed. I believe you have to have them drilled out slightly to fit our mounts. I never heard of a problem with them either.

Who uses them?