I used a GP 1.20-1.60 mount on mine to mount a os 120ax. I cut it down to fit inside my cowl. I only used it because I had it laying around... If your firewall is just the stock ply wood I would laminate an additional 1/8" 10 ply aircraft grade to it prior to mounting. If your's becomes to nose heavy mount your elevator servos in the tail. It is an easy mod and it makes the elevators much more positive.

I had to mount my engine quite a ways forward to get it to balance.

There is a lot of info in my build thread > [link=http://www.rcuniverse.com/forum/m_9018718/mpage_1/key_/tm.htm]Goldberg Ultimate Build 60 size by twn[/link]

I wouldn't use the kit supplied mount for a 4 cycle ys. It is designed for a 60 2 cycle.