The 5 flywheel bolts on a type IV bus engine have always been hex head.

#24 here, are the 5 HEX head bolts for the flywheel:

Look at the bolts that hold the pressure plate [clutch cover] to the flywheel: #3 here, are the 1.7[210mm] and 2.0[228mm] 13mm headed 8x1.25 clutch cover bolts. #30 is the torx 7mm 1.8[215] clutch cover bolts:

8mm with a 13mm head = 210mm flywheel
7mm with a triple-square head = 215mm flywheel