10.4.3 Classic Sixties – updated verbiage:

Triumph T100 unit-construction. Triumph unit-construction twins must include the following:  The cylinder head must be of the pre-’67 “squishband” type. The maximum carburetor size is 28mm, and bikes must conform to all other Classic Sixties rules.  Results in this class for 2020 will be reviewed.

AHRMA Handbook