RE: Goldberg Ultimate 10-300 build
Hi Mono Wing, time to change your alias!!
As you have read, I just finished up my Ultimate with a Saito 150 a few months ago. I used a Dave Brown mount and have the Saito set back to the firewall as far as it will go. I did not move the firewall back nor add weight to the tail. But, I did have to slide my 5 cell battery pack down the fuse toward the tail a bit, though, to get the cg right. The battery is mounted on a 1/8" ply stick that slides down the fuse into a slot and is screwed down to a block mounted to the former just above the lower wing. I got the CG spot on this way. I have never used the Dubro soft mounts, but if that mount has the engine much ahead of the firewall, you will have cg issues.
Regarding the vibration. There may be more on the 150 than a 120, but I don't think it is a whole lot more. Make sure you toss the light ply firewall and put in a good 1/4" or 5/16" ply firewall and reinforce it well.
You will love the Ultimate with the Saito 150. I have only flown mine a handful of times, but it was great fun!
I'd be happy to help out where I can. Let me know.
Ken