Wow.
Some one dug deep to find this stuff...I am glad it has been of some help. The article I wrote up didn't have the bulk of the 4.0 HO mod work in it. The AMC Forum posts contained more info that was written after the article was written.
A few updates..
On my Rambler (66 convertible) 258/4.0 HO head motor I put in larger valves 2.02 in, 1.70 ex (I think thats right, the exhaust may have been bigger), notched the block for a big improvement in low lift flow on the intake, shifted the intake valve .040 or so towards the exhaust to improve flow and to clear the cylinder wall on the bored 258 block to give me .027 clearance from the valve to the bore at .493 lift (not a problem on the 4.0 block). I kept the valve stems the same size, used roller rockers with lash caps and then added long primary tube headers (Clifford custom) and 3 45 DCOE Weber carbs. The cam is a comp cams 4x4 extreme dual pattern. The car is a monster and pins you to the seat from 1000 rpms up to the red line of 5750 (#5 rod journal will break at 5900-6000 if you keep it there very long).
I was in a huge rush to finish up the motor and get the car on a transporter when I moved to So Cal in 2004, move back to Va last August. Believe it or not I never put the finished head (larger valves and 4 angle grind) on the flow bench when I finished it and I didn't make any port castings. It took the machinist over a month to finish his work on the head but it was worth the wait. I don't have final flow values for it. If I ever set up my flow bench again and I have the motor apart I will flow the head. To say I regret not spending a couple hours to do this back then is an understatement.
1 bolt,
I am living in a rental house and porting is a very very messy job. My flow bench is not set up and my air compressor isn't set up either (ie I cant do any porting or flow bench work right now). I would be happy to meet with with you, share my notes and help you port the head at your place.
For a high rpm motor and a big cam the extensive porting is really worth while but for an off road motor bigger valves, and a lot of easy cleaning up of the bowl, throat and flashing will give you big benefits at lower lifts and lower rpms. I wouldn't suggest doing much to the runners so you can keep the velocities high for low rpm off road work. This is the sort of stuff you can do with a drill, a couple of cutters, a cheap abrasives kit and an Dremel with a flexible shaft. Send me a PM and we can set up a time to meet.
John