I know I speak from a position of being a fabricator, so it seems 'Simple' to me. Then again, it really is pretty simple. Just like any other swap it's all about adapting, and here all you need is to widen or narrow an opening, and relocate bolt holes according to the piece you use to widen or narrow with.

If a guy sat down and test fit & measured everything, then made up cardboard templates, then all that's needed is to fab the simple adaptors. This can be as easy as picking up some surplus steel, tracing out your lines, dropping by your local welding shop & having them cut, for cheap! Drill your own holes, for cheap! Bending can be done in a bench vise or with hand tools.

Surplus steel places have an amazing assortment of pre-formed shapes like square tubing or channel, in various wall thickness. The right piece of square tubing of correct wall thickness might only require some simple cuts & a couple of bolt holes, maybe even hacksaw & drill type stuff?