actually way long times ago, Meyers and Diamond were seperate companies. but Meyers bought out Diamond back in the early 70's i think it was

 

Actually Fisher plows look like no trip in 48 when they first started and early 50's, the trip edge was a 1957 innovation.

Snow Plow Companies - Fisher Engineering - History

Meyers has been around since 1926.
I know where a 1947 Meyers plow is, full trip.

Western looks like a newcomer in 1955.

50's model Fishers also used the under hood belt driven pumps.

Around here Meyers and Western were all you could buy in the 60's.

I also agree, a clutch of some type would be a fine addition to that pump and a cooler on the return line would also be another fine addition.
I bet that is some hot fluid after several hours of plowing.

 

i use to work for a co. called Lesco and i installed a lot of
Curtis plows we were kinda their gineau pigs when they hit the market
working out all the bugs for them spent hours on the phone arguing for warranty