I've never seen a Colt 22 conversion unit w/the split 2 piece slide like that.
But IIRC, Pachmayr used to market one that was built like that and was made in (W) Germany.
Seems like it was available for other pistols as well like the H/Power and Model 39.
Maybe this was a R&D piece for those units or another 22 Bullseye conversion.
Just going by memory,,which isn't what it used to be..