It is most likely a New Process 205 transfer case.
new process gear or "NP 208" other transfer cases of prior years are: NP 203 - Full time 4WD. NP 205 - Cast iron gear driven NP 208 - Aluminum chain driven
standard 80-90 weight gear oil will work if it's a gear-driven case, like the NP 205 I'm not sure about the belt driven type (NP 203) but I think it was a bit lighter weight
It is left of center
72- 76 150s and broncos
It should be a 205 new prosess NOT.......... the 700R4 was not used with the gear drive NP 205, only earlier trucks with Turbo 350's or 400's it is more likely a np 207 chain drive
While the best is subjective, a quality 4x4 with a transfer case is the 73 to 87 series of Chevrolet trucks. The dependable New Process 205 transfer case is designed to withstand high toque and horsepower.
Advance adapters makes a kit.
To install a shifter linkage on a NP model 205 transfer case it takes a few steps. Start with a new gasket positioning the transfer case to the extension, install the bolts and nuts, connect the shift rod to the shift lever arm, secure with the spring and washer, connect the front wheel shaft to the case, connect the rear axle and then you are done.
205-series and 208-series
203 versus the mighty 205 well well well I'll tell you what i know thru experience i have a 460 powered Nissan patrol far from stock it is used for rock climbing hill climbs outback challengers ect i first used a 203 as every body conned me saying good tough box, if you treat your 4by like a girl then their great if you want a serious transfer then the 205 is the way to go,
I've ran a number of the New Process 205's in various applications. If it is going to be used solely for off-roading I recommend an inexpensive 80W90 as it has the right properties and is easy to find if you have swamped it. For daily driving I would run a 75W90 synthetic as it will provide a little better wear protection and will not degrade as fast. Just remember this is a gear driven transfer case, under higher load conditions, your oil will break down quicker.