we went through this about a week ago, it seems that all the flexplates for the 4.0/4.2 block are the same except for how they work with the CPS, which is dependent on the ignition system. the Renix (87-90) flexplate won't work with the HO flexplate because the CPS is different. the 4.2 doesn't have a CPS (right?) so i think it would be safe to say that the 4.2 flexplate won't have the proper CPS stuff for an injected motor.
if you need an HO flexplate, I have one in perfect shape. I'm swapping an AW4 and just found out on here last week that I need the older flexplate ('94 tranny, '88 4.0) so I went a bought a new one. I'm in Michigan also, Jackson. PM me if you want it, I'll let it go pretty cheap.