Early Speed Twins, with six bolt cylinder base
Speed Twins, 500cc, rigid frame, eight bolt cylinder base
Pre-units....generic term for all non unit construction twins, 500 and 650s
Swing arm preunits.
Duplex preunits 1960-62
Unit construction, sidebag oil tank.
OIF. Oil in Frame.
Long rod engines, pre unit and unit
Short rod engines
Electric Start engines
Late 650 Thunderbird, short rod engines. (reduced bore)
Lots of other subgroups, Daytonas, Bonnevilles, TTs, but these are individual models.