I'd have to see a photo of your cabinets to be certain, but in our case, there was no modification necessary. I do have the service manual for 1974 models, which was incredibly helpful, especially for the uninstallation procedure on the RM77.
The RM2820 is much lighter than the RM77 unit, which is fantastic.
From a dimension standpoint, the RM2820 cabinet is very close in height to the RM77, however, there is a 2"H x 24"W electronic control panel bolted proud to the top of the refrigerator. You'll end up completely removing the living room bulkhead (not a big deal, just a few wood screws hold it in place) and then the long top shelf over the fridge will be loose. We went the extra step to completely remove the top shelf, so gain access to all sides of the refrigerator and to clean the wall panels that you otherwise cannot get to.
The RM2820 fits perfectly into the original factory space. The RM77 was held into place with many more screws than you'll find required for the new unit. Two toe-kick screws go into the floor at a very shallow angle from the front, two 5/16" x 1.5" stainless lag bolts into the floor from the back of the unit (through the service port).
The electronic panel, in our installation, nested inside the quarter-round coping/reinforcement extrusion that runs the full length of that top shelf. It will capture the electronic panel to within 1/16" - 1/8" of the buttons.
From a wiring standpoint, we took 12V
(for sparking the gas operation) from the closest living room cigarette lighter, which was idle in our unit. You may have 12V
already at the fridge, but we couldn't find it.
The one mystery of the installation, which I will eventually resolve, is the seemingly unused blue wire that is on the RM2820. It is dangling near the 12V
+/- terminal block and I'm not sure of its purpose. If anyone has an idea what it does, let me know! Otherwise, I'll call Dometic to see if they have an answer.