should be a good swap, crazy cheap on fuel too. the worst part will be the motor mounts, as the
trans im pretty sure is the same center section as the one in your gas truck, just swap off the tail housing (really really easy!) and it'll mount right up to your factory
tranny mount and the stock driveshaft will work too. just cut the engine mounts out of the crashed 84 and weld them in where they line up on the frame in the 91 ( you'll most likely need to cut out the stock gas engine mounts as well). its always possible that another thing comes into play as well, the best bet is to first swap the tail housing, bolt up the crossmember and sit the engine in place while its hanging from something and see how close the mounts are
i've never done this swap before but i've done enough into mazdas
__________________
93 b2200 F2t swap
build thread sold
92 B2600i with a 82 3.0L 5cyl 617 benz Turbo Diesel
build thread 
91 b2200 fully airbagged, 4 linked, 1/2" lines, lays frame
rebuild thread sold
91 b2200 v8, toy axels, 39" tires
thread sold
91 EF Si, B18a1 swap, etc...
build thread
'̿ ̿ ̿'̿'\̵͇̿̿\з=(•̪●)=ε/̵͇̿̿/'̿'̿ ̿
