I am really unfamiliar with American trucks, what engines were available for the 350?
EDIT: Just found this post:
Smarty wrote: ↑07 Sep 2021 21:22 Far as I know, the diesel 350's would've been H/NH(R)(S) and maybe C/J on the low end. Gas or butane was still the go-to for power/torque, and so something like a Hall Scott 400 was probably king at the time. I wouldn't be surprised if Continental was an option. It's just too bad that the engine model in ATS is so diesel-centric.
Any 1693 in a 350 would be a later re-power. The 350 only lasted til around 1957 or 58, and the 1693 wasn't being used in trucks until something like the late 60's, if even that early. I'd be quite surprised if a GM Diesel was original equipment on a 350 either – I don't think they had a lot of on-highway presence outside of GM until the 60's.