Barry-ct, what is the source of your info? I'm curious cause its backwards from everything else I've found on the truck engines.
I thought 8RT was the truck head, used thru-out the production, except maybe in 52/53.
Ford's habit of superceding numbers doesn't help us sort things out either.
And for all you car guys, trucks got the late engine in 1948. January 16, '48 to be specific and the 48 Bonus Built trucks have a unique serial number, contrary to the info on Mac VanPelt's website. Truck serial numbers that year begin with prefix 88RC or 87HC. This changed to 98RC and 97HC for 49/50 and maybe early 51.
It doesn't help that the shop manual for bonusbuilt trucks is 1949-51 w/ 52 supplement. It's like the transition year for 48 never existed - except for the serial numbers on 140,000 trucks.