I tell you what, send me an email to
dusty@wcb4x4.com to remind me tomorrow and I'll send you back a discounted price on the adapter plate that should make it worth your while to buy rather than make. Just tryin' to help a Newbie out
If you still want to make your own you really don't even need a drawing. Just take a piece of cardboard and transfer the bolt pattern from the frame to it, as well as the bolt pattern from the box. The new box holes will be slightly below the stock holes, but you can hold the box in place against the frame or take some measurements to get it in the right ballpark. It does not need to be exact. Transfer the pattern to a piece of 3/4" plate, then drill and tap the holes to 1/2"-13.
Or you could install it without the adapter plate, just use the front hole of the stock bolt pattern, and drill the other two holes to match the pattern on your box. You might want to reinforce the frame at the same time.
Good luck,
Dusty