Cobred,
Check out this link:
http://www.erareplicas.com/427man/jagrear/hop.htm
Also, you may want to email or IM ERA626 here on ClubCobra. He tells me that he recently made some changes to his ERA including changing the pinion angle. He said it solved his wheel hop completely.
I have an ERA and I bought one of the watts kits that Decooney developed. It helped but never completely eliminated the wheel hop. After breaking a u-joint that I believe was caused by excessive wheel hop, I bit the bullet and upgraded to the ERA rearend. That solved the problem completely but the upgrade wasn't cheap.
Chris