I picked up a ebay pipe for my DT2. It came with what looks like an oem muffler stay but there is only one hole in the bracket and it’s about an inch short to reach the rear shock bracket.

Something looks incorrect. The pipe fits snug everywhere else, just wondering if this bracket fits under something or it’s the wrong part all together?

I have a couple 1975 MX400’s and that looks like the broken half of the muffler stay, kinda common for them to break in half due to the rubber portion being old and brittle. I included a eBay link (not mine) of a guy selling his old ones so you can get an idea of what they look like, he has several pictures posted for reference, there are a few sellers with new ones for sell, not sure if they are correct for your bike model though?
75-76 MX400 YZ400 YZ MX 400 OEM EXHUAST MUFFLER HANGERS BRACKETS Buy It Now

Had to replace half of the one on my DT125B (1975) Enduro. Not hard to do, even having to fabricate the other half. Maybe some of the boneyards have one?