"Has anyone tried using J-frame parts on I-frame guns?"
It depends on the parts. An I frame has a flat mainspring, an improved I frame has a coil mainspring, and the J frame is larger in size to fit the longer cylinder.
Some internal parts will interchange.
The best thing to do is to either check with the larger parts dealers or go to a gunshow and take your revolver with you and find a parts dealer that is willing to dig through and compare parts for fit.