MARC using NJT equipment

I heard that MARC used Arrow MUs and maybe a few other cars can someone confirm this?

I've never seen or heard of NJT m.u.'s. During the late 1980s and early '90s, MARC leased a lot of power and cars, some just for testing -- from Amtrak (both electric & diesel locos), CSXT, GO Transit, and VRE among others. Included was NJT diesel 4131 in 1989, but that's the only NJT equipment I know about.

There are pics of the Arrow IIs during the Conrail days running on the Penn Line in the PC section of the Fallen Flags site. Could that be what you are thinking of?

Also, Amtrak used to regularly lease NJT m.u.'s over Thanksgiving weekend, and these would routinely show up in Baltimore and Washington.

After the Arrow IIIs arrived on NJT property, but before the voltage change on the ex-DL&W lines, NJT had a surplus of electric MUs. So NJT leased some of their Arrow IIs out to MARC so they could phase the Arrow IIIs into service.