Trans swap!

[jel111]

I have a question for the guys that have kept there inline 6. I want to keep my 230 for a while and see how the gas prices go or at least till I get a beater. I have the stock 3 on the tree and I wanted to go with an automatic. I picked up an axle with posi and a 3.90 gear. I want to go with a 700r4 as I see a lot of guys on here do. My bro says he can get a turbo 350 trans already rebuilt for bout 700 bucks. He says I should go that way anyhow. He says it won't make a diff. I say there has to be a reason all the posts I see on here go with the 700 trans. What do you all think and can I mod the old column or use one out of a newer truck that isn't so expensive as these replacement models?