The 3/8lp/picco rim actually is slightly larger than the standard 3/8". 1.436" vs. 1.381 on the pair I just measured. I remember running across someone saying a worn .404 pitch rim works. I actually turned one down in the lathe and it seems to work. I still would like to find a 3/8lp/picco rim for normal small splines.
I did run 3/8lp on a regular rim with a 525 jonsered. I left the chain slightly loose and it worked. It never seemed "right". No noticeable wear on the rim or drive links after about half life of the chain. I switched it back to .325.