Depends on the couch...
Most of the couches of that vintage were "knife-blade" style, where back flipped forward and rotated to make bed. It was possible to flip back rest forward, and then lift seat up (it was hinged with pins/bolts at rear on sides), and then get to fuses and univolt/power supply behind sliding storage chest under couch... It might be easier to get at for extensive work to remove couch (hold-down bolts along brackets on either side of hinge pins at rear of couch), but you could change a fuse without removing it... "Gaucho" couches lifted from front and then sort of expanded flat, but it is also possible to get under them by lifting and propping seating surface up to get at fuse. Again, for extensive work, rewiring or mods to Univolt, it's probably easier to remove couch..
I believe that vintage did use glass/tube fuses, and owner's manual should spec amp ratings, which varied by circuit.. There may also be a separate panel in rear where 110V power inlet comes in, and circuit breakers for main electrical circuit are located.
In Theory, there's no difference between Theory and Practice, but in Practice, there is usually a difference...