Hi Mikie, I am using a 61FX and APC12x6 with great results. I replaced the stock mount with a Dave Brown. I also have 2deg of right thrust built in using an Ernst thrust plate sandwiched between the mount and firewall. To answer your question : you can mount your engine mount on the firewall and continue with the rest of the fuse build. When you get the engine, find the best position on the mount beam to give you the right cg, and mark the bolt holes. Remove the mount for drilling. I have a 1400mah NiCd under the tank to get the cg at the rearmost position of the main spar without any additional lead weight. The 4*60 builds tail heavy. Search this forum for the many good threads on building techniques and color schemes for this popular kit