I bought this used JCM 900 cab that was modified with a birch plywood back and was ported. ☹️ The input jack was also replaced but it doesn’t bother me. -Because I don’t want the port, my original thought was to somehow plug/fill the port and tolex the back. -I’m now thinking that it would be easier to just replace the back with particle board or MDF and tolex it. Any thoughts? Also, did the JCM 900 cabs have MDF or particle board backs? In any case, I plan to install the 2x2-inch support (whatever that’s called) that was missing from the cab.