Looking to fabricate my own engine mounts,have some questions.

That's what I was thinking about doing. And agree that reference points could be lost if not marked or jigged carefully. If references were not lost. Did ya see a down side to that approach?

No, I didn't see a down side to it. I've got a jig to bolt a k-member to. Actually I have two, one that uses the frame bolts and one that uses the LCA pivot pin tubes. I had considered at one time making a bracket that would locate the saddle without having to measure each time. In the end I just didn't make enough of them over time (probably less than 50 in the last 32 years) to warrant that effort.