The factory 3 speed was a Muncie SM-318. There are lots of them around- - - -at last count, I believe I've got 5 or 6. There are very few variations other than the length of the output shaft and some differences in the side cover and shift levers from 1955 to the mid-1960's. There's a 3 speed overdrive version of the same transmission, the SM-319 that was an option on most cars- - - -not sure if it was ever installed in pickups.

The 283 engine was original equipment from 1957 through the early 1970's in cars and trucks, with a very wide variety of options from twin 4 barrel carbs and radical solid lifter camshafts on Corvettes to heavy duty trucks with governors, intended to run wide open throttle hauling heavy loads all day. "Returning it to stock" will depend on your interpretation of what "stock" means. Have fun!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!