I can't help you with plans, but it makes a difference if it's a reed valve or a TD.
What he said. If it's a PeeWee .020, something like the Queen Bee would be great. I know there are several more designs on Outerzone for a .020, but I'd have to go home and look in my .010/.020 folder on my hard drive.
If it's a TD .020 in good shape, it'll fly any of the smaller 1/2A planes designed for a Cox reedie or Babe Bee. Note that I said smaller, not the designs that would be marginal on the lower powered .049s. Those little TD's are stout engines.
Mark