The 216 engine and the early Power Glide engines had about equal durability.
They both did best with highway driving, regular oil changes and engine speeds of under 3000 RPM.
In my part of the country they could use an overhaul by 50,000 miles due to oil consumption which was caused by the oil ring and oil return holes in the piston plugging up with carbon. A highway driver could get double the mileage. The babbited rods would not be a weak point if oil was changed and , especially on the before 1948 models, rods adjusted it beginning to make noise.
I drove those engine hard and fast and never has any rod bearing problems.
Getting 80,000 miles on a mail route engine sounds about correct (with oils back then).......as the stop and go driving is hard on both the brakes and egine.
The 1953 Power Glide and all 1954 engines had full pressure oiling and alumimum pistons many lacked the low oil consumption that a cast iron 216 or 235 could provide.
Note that the 1948 and later dipper 216 and 235 engines had the thin babbitt bearings and with proper oil changing could go 100,000 with out a rod adjustement.
Wnen I first started at the dealership in 1950 we were overhualing 1947 engines with 35,000 miles. They were using oil, due to carboned up rings needed a valve job. wrist pins clucking at idle speeds, etc. After that low mileage and only three years the engine was fillled with sludge and the oil pump screen was beginning to plug-up.
On a lot of other makes tthe engine would be worn out by 50,000 miles and would require a rebore job, etc. to cure problems. A chevrolet engine could be overhauled once or twice in 100,000 miles and still no major cylinder wall wear.
My present 1950 Power Glide car has 56,000 miles on it, most with good modern oils, head has never been off, oil consuption at high speeds less than 1000 miles to a quart and runs as quiet as they did when new. 65 MPH is my usual highway speed with the 3.55 rear end and engine speed about 2800 RPM.

Gene Schneider