I realize this is long, long after you posted these questions, but if you're still here and interested:
1. I am Bill Hegarty's second oldest son (out of 13 children in total). My younger brother James, younger sister Alice, and I took over Hegarty, upon our Father's death in 1989.
2. 1965 was the first summer (after 8th Grade) that I actually worked at Hegarty. The 1945 Mack "LM" (once upon the time, one of the most powerful in Mack's lineup) was by then only a "legend" at Hegarty, since it had been sold years before 1965. My best guess would be it was likely sold, as part of a significant restructuring of Hegarty around 1962.
3. If the 1967 Autocar has the OEM black on chrome plates reading "Autocar-Diesel" on the sides of the engine cover, it was originally purchased and configured as a dump truck by Earl Williams, owner of North Hills Construction, East Hanover , NJ. After Earl's death, Hegarty took over North Hills and later converted it to a tractor.
4. If the sides of the engine cover are simply OEM chrome plated "Autocar" trim pieces, then it's one of a pair of used dump trucks, purchased by Hegarty for use alongside the above, in a gravel pit operated under the North Hills name in the lates 60's thru early 70's. Ultimatly, one was sold as a dump and the other converted to a tractor.
5. Regarding the 53 Sterling, although my memory is not the best, I believe that it is either the one sold around 1965 or another that Hegarty gave to Anthony (Tony) Ferrioulo owner of A. Ferrioulo & Sons of Whippany, NJ, in the 90's. The later has a cummins engine that was installed by a shop in Port Jervis, NY some time in the early 70's.
6. Unfortunatly, I do not have any photos of the above.