I would add that while you're on the inside, staple back up any insulation/foam that's come loose/fallen down over the years. I also might add a little bit too. The foam eggcrate looking mattress pad works great for this. Does what it's supposed to do as far as sound goes and doesn't make you itch. A lot of old cabs I've come across usually don't use enough. I'd line the sidewalls, back, top and bottom. The front board where the speakers are mounted you can leave bare wood. The stuff helps to reduce cancellations from soundwaves bouncing around inside the cabinet and generally makes it sound smoother/less woody. A sheet made for a full size (not queen or king) size bed is enough to do a 215 cab and can be had at target/walmart or wherever for 10-15 bucks. If the speakers are mounted with T-nuts you can probably put them back just where they were. If they're mounted with wood screws you may want to rotate the speakers and inch or two and drill new pilot holes to screw them down snug in some fresh wood. If the new speakers don't have a gasket on the back of the rim where it seals to the wood, get some weatherstripping and go around them or use some type of thick cloth/thin carpet to make the speaker seals against the wood. You don't want any air to leak out anywhere except the ports, where it's supposed to. Put a little caulk/silicone where the jackplate mounts and anywhere else anything mounts to the inside of the cab ie; anywhere anything might leak air. Also, if there's not a brace in there already, I would add a 2x2 front to back. Glue and screw one end of it to the baffle (front) in between the two speakers and then do the same to the corrosponding spot on the back. Ex. if the cab is 14" deep inside, take a 14" piece and put it front to back right in the middle, in between the speakers. More solid = less cabinet vibration which means more sound going out the front where the audience is. Any vibrations in the cabinet takes away from the end result which is sound getting to the peoples ears.
