Peco track is different -- their code 55 is in fact 80 of rail with two sets of flanges, the lower "25"'s worth buried in the ties to make only 55 visible, which solves various problems. (1) it's as strong as code 80, (2) the ties don't have to have as high plastic bits to hold the rails on so you don't get problems with large flanged wheels, and (3) the rails meet exactly, you can just use a normal joiner to join 80 and 55 at any point (the ties step up rather than the rail head, if you see what I mean).
Anyway, code 80 to 55 converters for Peco aren't going to be any use to you for Atlas track. As was said above, just solder your joiner to the 80 track and sit the 55 on top, blob of solder and Bob's your auntie's live-in logder...
Charles