Ron's cars would need a little adaptation (if possible) to maybe add 6 wheel trucks to the combine,coach and observation. That alone would help the cars look more like Frisco heavyweight cars.
AM's six wheel passenger trucks will fit just fine under the combine, coach and observation. They all use the same underframe molding and there is a mounting location for either truck.
It's a little hard to tell, but the two coaches below have been retrofitted with six wheel trucks while the KGB's "cabbage" retains the four wheel trucks:
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Update: I dug through the archives and found a broadside shot of the coach with 6 wheel trucks.
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The cars DO look much better with six wheel trucks.
Rusty