If you are talking specifically about the differential, then the answer is yes, but only if the two trucks have the same model of axle, and you also switch the axle shafts. If you are talking about the entire front or rear axle, then this is also possible. All straight front axle 4 wheel drive Chevy truck front axles can be interchanged (some will need conversion u-joints in the front driveshaft to connect). Also, 73-87 (and 88-91 blazer and suburban) rear axles can also be interchanged, with a caveat: 1 ton trucks have different rear axle spring pad spacing, and the 1 ton rear axles will not fit 1/2 and 3/4 ton trucks without cutting, moving them, and re-welding.
what is stock differential ratios for a 1979 gmc jimmy
Yes.
dexron
in the transmission
No, Nothing will line up are even match up.
with a torque wrench
yes
Check out this site, http://www.nadaguides.com/
Rochester Quadrajet.
That is the ignition coil.
www.usedpartscentral.com/used_chevrolet_parts.htm and www.ebay.com are two places where you should be able to find a seat for your 1979 Chevy.
Who said it won't ? It will fit right in there with NO problems