Originally Posted by vstech

Whooo boy. good questions all.

77-early 79, a/c was the york monster and the glow plugs were the old loop style needing conversion plugs to have fast glow.
mid 79 the a/c was changed to GMR4 but the plugs were not changed until late 79 to the pencil type
turbo was introduced in the 81 year vehicle, and at the same time it got the digital speedometer and 722.3xx transmission to handle the turbo, in 82 the trans got changed back to mechanical speedometer, but stayed the .3xx to handle the turbo. 83 the plastic fan was added for better cooling, but not the smaller wp pulley that the SD got the same year...
in 81 and up 123's the gear ratio was changed taller to better take advantage of the turbo's power, 3.07 for 81-84, and as mentioned 2.88 for the 85 year.
I'd like to find an 81, but I don't think it'd be better than an 84 from the updated standpoint.
85 I'd think would be the ideal year to buy. best power, and economy of all the years.