Here is a 1975/76 Sno*Jet track and suspension. It can be mounted right under any older slide suspension snojet. It fits into the stock holes, but you may have to also swap drive sprockets. The same thing can be done to the older bogie suspension Sno*Jet, but you'd have to reinforce the tunnel and drill holes to mount the suspension.
Instead of using an old Sno*Jet track, use a 121" Polaris or Bombardier track. The only thing is you'll have to change drive sprockets, and extend your suspension a couple inches
As you can see, the new suspenion fits right in replacing the older multiflex suspensions. With my sled, the track wouldn't quite tighten all the way, so we took the tunnel supsension brackets off a 75 and mounted them on my 74, giving more lift and tightening the track.
From left to right, the stock 75 SST Suspension with a new Bombardier track. Next is the 74 SST with the multiflex 75 suspension and brackets to lift the tunnel. Beside it is a 74 SST, suspension and track are both stock except the suspension straps were lengthened slightly. Note how much higher it sits up from the bone stock 74 SST to the right.
You also might want to consider trying a 133" track