Having had a broken engine mount a few years ago, I can say that early RV-6(A) engine mounts were manufactured by a different vendor than the one that is presently used. A new JIG to fabricate the current RV-6,7,9(A) engine mount was created by the current vendor for all the new production. The same engine mount is currently supplied for the RV-6,7,9 builds and replacement. I did replace the engine mount but I paid to have a custom engine mount that was built from my damaged mount. It was reported to me that my old mount was 3/8" longer than what a new production unit would be. The main four mounting points to the fuselage was the same as what the new engine mounts were.
IF you are replacing an OLD engine mount on a flying airplane, there MAY be some issues with cowl fit behind the prop. IF you are in the process of building and the cowl still needs to be fit, build on.
I do not work for Van's Aircraft and my above post has been my experience.