Transmission Question for a Bel Air...

I have a 1956 Bel Air with a 350 and the original 3 speed manual trans that has been moved from the column to the floor.  I would like to put in either an automatic or a 4 speed but it seems like the local guys are resistant to the idea.  They like the idea of just rebuilding the trans I have.  What is best for me to do?  I don't have tons of disposable cash so the idea has to be reasonable.  THanks so much.  

if you change the tranny to either a a 4 speed or an automatic you will have to have the drive shaft shortened which is going to cost you some to. With todays gas prices I would say a 4L60 but not the 4L60-E. the 4L60-E requires a computer where the 4L60 doesnt a simple lock up kit for the torque converter is available. The 700R4 and 4L60 are almost identical the cases are the same the difference is in the input shaft and check balls in the valve body. I rebuilt the 4L60 in my 92 Silverado  2 years ago, NAPA has a great rebuild manual for it and almost all GM automatics, It litteraly has a large picture with arrows pointing out what you are doing for each step. I found a company i believe out of oklahoma that specializes in 700R4 and 4L60's, their website is transmissioncenter.net I ordered all the parts that they put in their "Raptor" 700r4 plus a B&M shift kit, the parts for their "raptor" transmission included upgraded clutches, new overdrive servo, pressure valve, and afew other odds and ends. Ihave put over 30,000 miles on it so far and it still shifts like a raped ape all the way into overdrive, there is no delay shifting into any gear. you don't have to have it as brutal shifting as I have mine, the rebuild kit I ordered came with different weight springs so you can set your shift as soft or hard as you would like. I chose the hard due to towing concerns. all in all i spent maybe 1200.00 doing it myself for the very first time. If you do decide to rebuild one yourself i would suggest the purchase of a transmission piston compressor, you can do it without it but the snap rings are a real ***