XP-1 developer was C-41 developer which mixed to working strength was pretty much C-41 developer 1:1, used at a five-minute development time. That dilution plus intermittent agitation gave slightly higher acutance.(posted 8590 days ago)BTW, it would develop color C-41 film ok too.
For experimentation, I'd suggest simply diluting C-41 developer 1:1 and giving it five minutes development. That should be in the ballpark.