Hello Bolters

; after reading all the past posts on transmissions (T5, Autmomatics, 4 speeds)I have decided that I like the idea of the three speed with overdrive. I would be like to install it in 56 GMC 1/2 ton with 270 engine, 3 speed trans. Every week or so I drive the truck to work (120 miles round trip, with the new 3:38 ring and pinion it runs along pretty good, I would like to increase gas mileage ($2.00 a gallon)and lower engine rpm. Speed is not that big of an issue. Hopefully some one can answer a couple of questions or provide ideas; I am not totally set in my way and can be swayed to a better idea.
First off; will the overdrive trans bolt up to my 270? Will current shift linkage work? Are drive shaft modifications required? What year and type of overdrive unit should I start searching for? If anyone knows of web links for this exchange please include them. Once again thanks for your support, your information is making my project much more enjoyable. Roy