Welcome!
I just got my first 124 wagon myself a few weeks ago!
this is the best forum period! you won't be able to find a different site better.
if it's been sitting, I'd not try cranking it first off.
78K is AWESOME!!! Mine was extrememly well taken care of, but it needs quite a lot.
I'd check the motor for stiffness by cranking over with a socket on the bolt on the crank pulley. if it's smooth by hand, it'll be safe to try cranking with a battery.
the issue with these motors is the fan looses viscous fluid, and can overheat and blow the head gasket or warp the head.
also the vacuum pump can fail and destroy the motor.