Advice needed, Knowledge requested please

[mdw]

Hi All,
Well, getting ready to dive into the 71, goals are to get a better performing, better mileage, and a new look family vehicle. In its current form it is a 71 1/2 ton with a 350/350 combo runs great with no issues. What I have done is I purchased a 89 pickup with a 350 and a 5 speed manual. My intentions are to couple the 2. I am looking for opinions on putting in the fuel injection system motor and all and replace what is in there now. I have also considered just swapping out trannys and making it a 5 speed to get the better mileage and the ability to tow it behind our motor home when traveling. I could go with an auto overdrive and find a shaft disconnect Any thoughts would be great and appreciated, THANKS!