This is a late 5 spd trans.
This is what you can do to make a short throw shifter.
The late 5 spd can let you make it a short throw shifter by drilling the upper hole and extending the bottom of the shift lever.
The difference between the 4 and 5 spd trans is the pivot point. The 4 spd is about 5/16" longer than the 5 spd.
'78 and '79 620 gas tanks are different. I had to replace the one in a '78 I had and picked one out of a '79. Both were king cabs. I'm not sure of the differences as I had someone else do the work. They had a '78 620 and took the tank out of that.
So I do have a '79 kc tank with a repaired dent available.
David Irwin rebuilds them, he is also the same one who makes the Parking light harness relays and headlight harness relays. If you haven't already bought a set of them, contact Dave and he can set you up.
I have not done this, but msa has a kit for the power windows. Make sure your window regulators are in top shape and well lubricated.
I am sure there are other manufacturers.
http://www.thezstore.com/page/TZS/PROD/classic08h01/50-4211
Looks like it's a Spal kit.