Well, Your source + all of Mine (3) call it out as a '78 A-999 L/U behind pass. car 360's. That's a loooong download of trans codes on the 'Dippy' forum, the DC/MP Chassis racing/reference manual, & @VOETOM 's excellent manual. If somebody had a 318 Dippy w/a failed non-L/U A-998, they may have came across the superior A-999 needing a rebuild, but didn't want the L/U. Hence the trans man swapped the needed parts including the fittings to match the lines in the car. I witnessed many wild things folks would consider far-fetched today, just for the daily ride, that is My best honest guess.