As long as your bottom bracket is a standard one-piece, you should be able to use the adapter sold by Sheldon. Alternatively, you can stay with one-piece cranks and replace the BB (cups, cones, balls, and all) with a bearing kit that costs all of about $16, also available from Sheldon. A modern crankset would probably really drop some weight, though.
I had to whale on those cups a little to get them to move when I did this. Flood the press fit with some WD-40, support the frame tubes on the ground with some blocks, and use a chunky (1/4") punch. Then really put some momentum into it. Once the cup starts moving, change the place you're hitting so the cup comes out square.
Good luck!
Edit: wait, wait, wait...how can your crank be cottered and one-piece at the same time??? The cotters are used to keep a three-piece crank together.