Then just rebuild the front end. I know it's not what you're used to (trunnion on top), but for what you're doing it's your best bet. The suspension is plenty strong, and the trunnion on top is probably NOT worn out. Ball joint has a lot more stress and may be. The only disadvantage to the trunnion is you can't get much caster. It's designed for ZERO degrees caster. You can get about 3 degrees out of it either way, but that's it. It handles fine with zero degrees.
The old AMC/Rambler GEN-1 V-8 weighs about the same is is just about as big as an old Ford Y-block or Chevy 396... maybe 50 pounds under that 454. The cast iron auto trans weighed more than that TH-350. If your car was a factory V-8 car you should be fine. If it was a six you just need stiffer front springs (even the V-8 could use that!). Stiffer springs will do more than a sway bar will on any high spring suspension, so if body roll is a concern get new front springs.
If brakes are a concern you can get a Wilwood AMC kit now, or go to www.scarebird.com
and order their kit. They sell you a special caliper bracket and a seal spacer, and send a list of other parts you can find at any parts store (GM calipers and Ranger 11" rotors). Will cost $400-$500 total for new disc brakes up front. If you want bigger you'll have to go with the Wilwood or an Aerospace Components setup ($800+). The 11" rotors should be fine even with the big block.
All this is cheaper and easier in the long run than trying to change the suspension. You'd have to cut most everything in front of the firewall out to use something like a Nova or Camaro subframe. You could install a Mustang II front end, but there is nothing to really gain over the stock Rambler front end with a disc brake upgrade. Note that the lower control arm/strut is practically the same as the Mustang II, just the upper part of the suspension is different.
The Rambler classic is the same size as a comparable year Chevelle (say a 64), a bit larger than a later model Nova, but not by much.