Thanks.

I looked at my 1988, but can't see (or recall) most of the water pump bolts vs. studs without removing the water pump pulley.

On the 1980, there are 2 bolts on the upper left (one holds the return line), 2 bolts on the lower left, and two studs with elongated holes on the right. I thought that arrangement odd, too, because the FAQs emphasized tightening everything equally in a star formation.

The water pumps for the 1980 and 1988 are similar, the only difference being the location of the bolt that secures the return line, 1980 being on top, 1988 on bottom, making them incompatible unless I somehow figure out how to invest that bolt.

All of my water pump bolts are starting to round out (I used 6-point sockets only), but I cleaned the threads and used anti-seize, so hopefully they'll come out easily next time I do the water pump. I have a spare water pump pulley nut, which is M6 x 1 and it fit perfectly on the studs of the water pump stud, so I presume that the bolts must be M6 x 1 x 30 mm.