Welcome to the forum Daniel!
I too have a '65. While in college it had a 250 6cyl with a 4 speed and later changed to an automatic. It was more street performance like TJ's, but I knocked down 15mpg in town with it back in the day.
There are few ways to get the power brakes and steering for your truck. I would keep the 6 for now if it is in good shape mechanically. I would swap in a HEI distributor and do a good full tune up with new plugs (larger gap for the HEI), and clean and adjust the carb. If you do swap in the HEI, the power wire from the plug on the firewall above the engine, has a resistance wire in it for the points distributor. That wire needs to be completely replaced with a standard 12ga copper wire to supply a full 12 volts to the HEI for best mpg and performance.
For power brakes follow this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=611577
For the dual master cylinder conversion follow this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=599582
While Sharps40 is no longer an active member, search his threads, he has plenty of info on what he did to get good mpg from his 6cyl.
For power steering, there are brackets available for the 6cyl to mount the pump, and CaptainFab has a bracket to mount the steering box to the frame:
http://www.67-72chevytrucks.com/vboa...d.php?t=332923
pump brackets: davisspeedequip on ebay
http://www.ebay.com/itm/10003-292-CH...wrv_jA&vxp=mtr
or:
http://www.ebay.com/itm/10003-292-CH...wrv_jA&vxp=mtr
Keep us posted on your progress!