I decided to add an engine support to hold back the engine and transmission during heavy braking. I know the engine package moves forward a bit because it has scraped a brake line guard in installed around the rear compensator and lines. Now when I hammer the brakes or down shift hard the engine and trans stay put!

I've never herd of that problem. On both my V8 914's the engine does not move at all. I would be more concerned with the structure holding your engine mount.

Well, I have a 930 box which uses a different rear support, and am using a Renegade cross-member which is (no offense ) not designed to hold the engine from moving forward or back well. I think they all move a bit your just not there to see it.

My mounts etc are fine, maybe just my set up is a bit different.

Good idea. The way the mounts are made usually allows for some front to rear movement. We used to put a chain on sbc's and sbf's to stop motor torque. A cable thats adjustable will also work and not transmit vibration.