The 8T's used the almost bullet proof D318 engines
8T 11013 (1952)
8T 13547 (1954)
8T 18527 (1956)
The oil clutch version (desirable) came in at 8T 16361-up
The 12E 99E8444 (1963) used the D333 engine.
Both engines had turbo applications but I can't say that I would bother doing that.
If condition and prices of the machines are close, I'd go for the 12E. If it still has the "buzz bomb" pony motor, it's real easy to convert to direct start. Another reason might be parts availability. .it's probably going to easier to find parts for the 12E.
As far as a turbo, I've never seen the need for one on my own 12E. .it runs out of traction in the lower gears before running out of power unless I'm really pushing it hard in the higher gears and/or steep roads shoving a lot of snow and this is at 5,000 to 6,000 ft elevation.
You have a wonderful day. Best wishes. Deas Plant.