The Reo M34 "Eager Beaver" appeared in 1953, and the M35 the following year. Both were procured in the early 1950's, but subsequent contracts were for the M35 only, and the M34 dwindled in numbers as they wore out over the next 25 years or so. Very few turn up in Vietnam photos.
The Revell kit is not a copy of the Monogram kit, it is the Monogram kit, which was originally released when the truck was actually in production. The molds are well over 50 years old, now, and the kit is very primitive. If you want an M34, your best bet is to cannibalize a few parts from the Revell kit (load bed and wheels, mainly), and graft them onto an AFV Club M35 series kit. If that's too expensive, (and you are a glutton for punishment), you can improve the Revell/Monogram kit with a lot of sheet plastic. The Eduard photoetch set for the AFV Club kit will have a lot of items useful here as well.

Yes, The AFV Club trucks are 1/35th.
Monogram's military vehicle kits (and even a UDT boat with divers) were all originally released in 1/35th scale in the 1950's (though some boxings claimed they were 1/32nd). Monogram pioneered the scale, long before Tamiya and Nitto. Ironically, Monogram zigged when the rest of the industry zagged, switching to 1/32nd for their new line of military kits in 1969, just as Tamiya and the rest of the manufacturers jumped to 1/35th.
The Monogram kits have mostly been surpassed by much better kits of the same or similar subjects from other companies,and there is little reason to buy them now, except as nostalgia pieces.
By the way, Revell also had a decent M35 truck kit of their own produced in the late 1950's, but it was in 1/40th scale.