Here's ya some reading material to get acquainted with the little 620's internal workings. This is 77 manual so some of the stuff that Mike mentioned that are features of the last couple years are not included.
I acquired our one owner '78 Longbed (believed to be 150K miles and it has all the good stuff that mike listed and 5-speed trany) five years ago with a bent valve. Replaced the valves and all the small ancillaries on the engine and it is pure sex to drive around town. Kinda like darting around in your favorite pair of britches.
That L-Series engine is an amazing little machine.