Oh, I looked into it already. I wanted to go the same direction you did - 4 cylinder engine onto wrong-species trans.
From what little I remember, one of the bolt holes was right. The ones at the "top" (deck surface) were nowhere near right, and at least one of them was flapping in the breeze instead of meeting the engine. The kicker is that 4-cylinder models mounted the starter to the transmission, while 5-cylinder models mount the starter to an ugly, beefy-thick ring cast into the block.
I don't think the particular 4-cylinder block I wanted to use had provisions for the lower block brace (essential for longitudinal) on the oil pan rails, but I'd been hoping to solve this with a newer cast aluminum oil pan, which would have bosses for attaching to the transmission.
Another thing I found out - 4-cylinder and 5-cylinder engines cant over at different angles! The fives are laid over more than the fours.
I wonder how strong the FWD manual trans was from the A4s. We probably didn't get many V6 FWD manual trans A4s but that might have the strongest US-sourced box. (I doubt very many, if any, of the rare front-drive A8s had manual transmissions...) A rule of thumb is that any longitudinal trans made after ~1992 is going to be dual bolt pattern. They started filtering in sometime around 1990 but the single-pattern units stayed in use until the end of the 5000/200 range.