Motorcycle Mechanics January 1972 has a piece ‘Making a Bantam Fly’, written by Brian Lecomber with input from George Todd.
There is a port tuning ‘chart’ which give the following dimensions - note: for full race tune add up to 2.00 mm to all port heights. The 175 figures are in brackets. Whether the widths are cordial is unclear. All port profiles are rectangular.
Inlet: 19 mm deep, 33 mm wide (38 mm wide) with 6 mm radius corners.
Exhaust: 19.5 mm deep, 32 mm wide (37 mm wide) with 6 mm radius corners.
Transfer: 11 mm deep, 23 mm wide, (28 mm wide) with 1.5 mm radius corners.
Carb: 26 mm Concentric.
Any thoughts on what state of tune this is compared with the latest ideas?