The RMs where two shockers, the CR 480 I believe was a two shocker, the YZ came later and was monoshock. In general pre 78 with the exception of YYamaha was two shocks. Check out AHMA ( American Historic Motorcycle Association) the have a MX section and I'm sure you could hookup with the correct info.
YZ400 and YZ465 were the under tank "mono shock" designs.
YZ495 was a early linkage design. Of that set the YZ465 was the best of that era in its class
The Honda CR480 was made in 1982 and 1983. Both were linkage single shock chassis. The 5 speed '83 was better.
The RM 400 of the late seventies was a twin shock chassis. The RM465 and RM500 were a single shock design. The 465 didn't have the raw power of the 500 but ran better and was the better of those two.