Only four '88-91 cars have manual gearbox.

POR 928 L WP0ZZZ92ZLS841528 1990
POR 928 L WP0ZZZ92ZLS842002 1990
POR 928 L WP0ZZZ92ZLS842006 1990
POR 928 L WP0ZZZ92ZLS842013 1990

All four have only few normal options without anything special at all. Last three were probably ordered at same time as usual practise was to buy several cars at once with different color combinations.

 

i searched a while ago to look for what trans to buy and listed this from a porsche book, may or may not be right

in uk s4 came with manual G28.12 / m28.41 or auto m28.42 from my87>
cs was introduced in 88 in manual only with G28.55 box with 2.72.1 and m220 lsd in uk 928 s4 SE was launched with the same box
89all s4's were auto and all gt's were manual box G28.12 or G 28.55
91 all cars had same cylinder designs and manual box received a shorter throw linkage
91+ gts had G28.57 box 2.73.1 or AT A28.18

 

Good up to 89.

In 89 both there were manual box S4's and the GT was introduced in around February '89. Even after the GT was intro'd, some S4 5-speeds were made and sold.

The short-throw shifter linkage was broadly introduced with the 89 GT - its one of the ways to distinguish between an 89 S4 and an 89 GT - S4 has a taller gear lever. (note - 1988 SE's also have the shorter throw linkage, not sure on Clubsports)

The 89 GT cylinder heads were modified S4 ones - during 90 Porsche changed their cylinder head production and all of production got the modified GT version including S4's, although only the GT's had the higher power camshafts.

Lastly, GTS was 92-onwards, although Porsche's production for the 1992 model year started in Sept. '91.

 

Several CS used normal S4 gearbox.

 

main problem i found when researching was in the s4 and > they seemed to have a general plan of what spec to use but changed it for either poor parts supply or overstocked parts so there were loads of combinations. They also changed the designation of models but didn't always upgrade all of it.
when the s4 changed to s4 and gt for auto and manual the engine spec of the gt changed twice in three months with cams/pistons/etc and the gearbox/lsd changed. To make it more interesting they then fitted whatever was left between s4's/GT's and claimed GT items on S4's were fitted as no cost options.

 

Agree, but yet to see a GT with 2.64 gearbox...