[Sean]

Cap 98 is the one closest to the power transformer of the two side-by-side electrolytic cans. There is a red wire that connects its center post to the left terminal of the filter choke 96. If you have the original 91 capacitor, it is wired as follows:
Blue terminal (positive of 8uF) connects to speaker socket via red wire.
Unpainted terminal (positive of 10uF) connects to chassis ground.
Case connects to case of cap 98, wire coming from power transformer connects to this point (center tap of HV winding).

Both caps 91 and 98 have the electrolytic negatives connected to the case. I am using 10uF 500V caps to replace the 8uF caps in 91 and 98 and a 10uF 50V cap to replace the 10uF section of cap 91.