Yes, it is easy to work with. You make a mold out of plaster of Paris in 2 parts so it can be separated, let it dry well and coat with a release agent. Then you mix two parts, pour it through the holes you made in the mold (two...one to pour into and one to let the rubber flow out the other end) and it cures into black rubber...as hard or as soft as you wish. As I recall you have about 10 minutes to pour the rubber formula in before it starts to set. Dead simple to make molds. Just remember to set pins (dowel rods with beveled tips work well) in the first half and also spread a release agent over everything so you can separate the two halves. I make a small box out of cereal box cardboard to make the mold in and then just tear it off when the plaster is dry. DO NOT USE WALLBOARD COMPOUND AS A SUBSTITUTE FOR PLASTER OF PARIS. Sorry for all caps but wallboard compound will not dry like plaster will and even when it does dry (very long time) it won't work because it usually changes dimension and cracks internally. It is completely different in composition and performance. If you do a good job with your mold, you can re-use it as many times as you wish. Actually I discarded the Cadillac motor mount mold around 5 or so years ago.
Do you know the shore rating of the enduro-flex you used? 90 to 97 shore will give you plenty of strength and will still dampen noise. Anything with a rating down to around 80 (shore A) ought to be okay. I would not use anything below that, however.
The Cadillac mount was one I made around 1992 and at that point I could not find one anywhere. I should mention at that point a pound kit of Flexane was around $25. I see the mount has been re-produced since then. This is what it looked like and one of mine had broken (the engine would lift up off of it when rpms were increased):
https://www.caddydaddy.com/1954-195...production-free-shipping-in-the-usa.html
