being a 50..the ratio is stock at 3.9 and only in the hilly country was a 4.1 an optional rear gear...find it stamped in place by brushing the passenger side of the hog head or the very top boss of the hog head..
Number of gears you can fidn to swap out..most however will require removal of your old leaf mounts and reweld to your donor unit in proper position to match the spring width and also take care to match your pinion angle..if transplanting a 318 or even better the 3.9 V6 as no firewall, rad support change will be required. The Dodge Dakota is a very good swap..see previous forum thread of last week on ratio available..hood tag will denote ring gear size and ratio. 318 and early A500 or A518 will give you 4 speed OD with just a override switch to connect to lock out...check with truck, ramcharger or van for this combo...very sweet setup..I just returned from a 1400 mile trip through the mountains pulling 5000 lbs both ways...OD was great...some idiot stopped traffic at foot of Monteagle so had to start without a running go..still topped the hill at 60 mile per hour..3rd gear...