I doubt you really want to solid mount your motor unless you're doing some serious track work - especially with an older engine. There'll be a huge increase in vibrations and at certain revs the whole car will resonate. Not to mention that all the welds on the car will eventually fatigue
Having said that I have solid mounted the motorbike engine in my kit-car - but I nearly didn't, I only did in the end because it's so well balanced - the balancer shafts on it are only needed on the bike to stop the mirrors shaking - doubt you could say that about a golf lump!
