Hi, i have a Kadet Senior, and have had several motors on it over the years. I just keep useing the existing firewall, but use new motor mounts each time. Occasionaly i have to drill new holes in the firewall to put blindnuts to hold the new motor mount. You could make a new firewall each time if you wanted, & just attach it to the existing one with bolts & blind nuts. I use the plastic radial motor mounts everyone sells, nothing fancy....Gene