[RSupdate]

While I am certianly not an expert, and Camgrinder will have the most accurate info, You will be limited to how radical a cam you can use pretty much by the fact you are using the DME Motronic ignition. The cam's duration will have to be right in the 112-113 area, which is a lot different than the early S cams you mention.

Assuming the JE pistons have preclearanced valve pockets in the dome tops, the next step up would probably be the Factory 3.8L RSR Super Cup Cams. They are only slightly more radical than your current 20/21 grind. check the lift & Duration #'s very similar.

I am running the 20/21 grind and the Mahle Euro 10.3:1 P/C's as well as a Steve Wong Chip tuned for 93 octane. I blend 50/50 100 & 91 octane for an avg octane of 94.4. I didn't twin plug so this is the price I pay to play with my toy.

Anyway, that's my .02.... good luck and keep us posted on what you end up doing.