It seems ERA uses the same mounts as LSC. I couldn't find urethane mounts either, so I made some. Here is my picture gallery -
URL to my clubcobra posting with pictures is linked.
Do you need urethane motor mounts? Here is DIY
The first pair was made with one time use plaster of Paris molds. I removed the vulcanized rubber from a new pair of mounts and poured in 80 durometer polyurethane. I decided to use the bolt thru as recommended by ERA as an insurance against failure of the mount. I used it on both the Left and Right. Just leave the bolt slightly loose and it has not impact on harshness.
I am finishing up some fiberglass molds and plan to make several sets of motor mounts out of both 80 and 94 durometer polyurethane.
I have had two ERAs and observed several others that the Left headers slightly contact the body. My theory is that the polyurethane mounts will stop the contact.
The contact seems to be caused by excessive stretching of the LH mount and excessive compression of the RH mount. The LH mount can be easily fixed with the limiting bolt modification. The RH mount is the tougher one to fix, without making it more resistant to compression.
I considered welding a limiting feature inside the motor mounts and than casting over it. Much like is done on many other cars. It is a lot of extra work and doesn't accomplish anything more than limiting bolts will do. Plus the limiting bolts are adjustable. If you tighten the LH bolt it completely eliminates stretching of the mount.
John