Mini-starter compatibility

I picked up a mini starter from a Dakota at the pick and pull. There was nothing left under the hood but this starter with the battery cable attached so it was just too easy to drag home with me. So when I went under my 67 to bolt it on my 273 I found a hardware issue... The bolt holes in the mini starter are threaded where the original starter has clear holes. after at least a year I still don't know if this is normal or if the strter I picked up was from some other vehicle and just thrown in where I found it.
Stock starter is still working fine so it doesn't matter much.
Good luck