Not so much 'Drop in' as 'Lift In with some mods'. If you get a 40 series 5 speed (or at least the top loader from a 40 series), then on an 83 you will be able to put it in with no modification to the floor pan. if you use a 60 series top loader, then you will need to move the shifter lever hole down about 3" (see photo) and bend the transfer case lever forward to keep the handbrake lever from hitting it.
You will have to shorten the rear drive shaft and lengthen the front. You will have to bevel out the top of the hourglass shape on your bell housing just slightly to fit the larger notches on either side of your input shaft on the H55 (easily done with a Dremmel).
Finally, you will have to either put a handbrake on the rear axles (easily done using the backing places from a 60 series) or use your handbrake from your own transfer case. You can built this into your new transfer case, or simply put your transfer case onto the back of your new 5 speed (if you do this, however, make certain that you install the little plastic drip lubricator- this clips into the front of the transfer case backing plate, and drips gear oil onto the 5th gear).
Are you on the troopy registry? The link is in my signature.
Cheers,
Josh