I plan to put electric brakes on our '76 Trillium
and had the RV place look at it last year. Ours and I suspect yours has the right axle mounts for adding brakes. A couple of points to consider:
a. Check your torsion axle by jacking up each side in turn and making sure it is extending and compressing properly before spending money on brakes. Changing the whole axle is also an option. My axle turns out fine but these are old machines.
b. My RV guy in any case first recommended changing the whole axle for a new one with brakes already installed as there isn't a huge difference in price. The axle on our '76 however is welded to the frame which would make it quite a lot more difficult to change. I don't know how your '77 might be mounted.
If you have a reliable RV maintenance place, they should be able to advise you on bearings/brakes/axles, and probably will order them for you, even if you decide to do the work yourself.