I am going to attach a few photos of the engine mount process.
The one below is of the mount being rough fitted to my RV6A airframe. The mount is only tackwelded and the top cross pieces are actually still loose. I left them loose so I could make some last minute small adjustments as needed. I was happy that I am only a few millimeters off of where I want to be. Nothing that I cannot correct with a few extra washers to get it just right.
The tubes are 4130 chromoly 3/4" and 0.49 wall. It will be primed and painted once the tig welding is completed.
The next photos is of the rear of the mount. Noticed the top cross pieces are missing. Also notice the grey colored mounting plates. These are made with 6061-t6 aluminum plate. Notice the top one has a piece of angle iron on it. This provides the rigidity needed to take the load. The bottom one has significant plate support on the front side that is not seen from this side view. You can see these lower plate supports on the forward side of the bottom plate in the picture above.
The last pic is the frame being tack welded on the jig. The bottom plate has the lower section of a Vans OEM mount as well as weldments for the rest of the frame positioned to replicate the pattern of the firewall. The top section is the jig that has the pattern of of the grey colored plates on the engine. The jig was created to properly orient the engine on the airframe. In my case it was a bit more challenging because I had to also position it to match a cowling I made. The end result will give me about 7-8 inches aft of the engine and also 6" forward of the engine. Saber Manufacturing is making me a 6" extension. It will have the 4" bolt pattern on the engine side to match the pattern on the Viking Aircraft engine gearbox, and a SAE#1 prop pattern on the prop side.
Feel free to ask questions.