Interesting, I had the EXACT same problem with the hoist I got from Harbor Frieght...the diagonal support braces were too short to reach the pre-drilled holes in the main support...
I just ended up drilling new holes that would fit. I've used it dozens of times now (lifting all-iron I-6, and even the entire front end of my old Cherokee

)...works fine. Besides that little issue, the rest of it has worked flawlessly.
This is the one I got....photo taken while I was fuddling around trying to figure out if I was doing something wrong in assembly when the holes didn't line up, lol..
Apparently the chinese don't understand the concept of "how things fit together."