The ZDZ 40 is a good match for the Sig Extra, I put one on mine this winter and love it. It was my first gas motor and definetly won't be my last. It's about the only plane I've flown all year as I just don't want to mess with the glow motors.

I would put some tri stock on the landing gear block, and firewall. I had reinforced the firewall but not the landing gear block and last weekend my gear block busted out. I think the more vibration from the gas motor had something to do with it. I did have a less than perfect landing but it should not have been enough to rip the gear out.