Reading off the drawings in the books.

1970 the engine centre line as the datum

The dry frame is 16 7/8" from the datum to the centre off the lower steering head bearing plane

1971 OIF

The swing arm centre is the datum line , this is approx 1.2 inches above the motor centre line, .
The 71 drawing shows datum to lower steering head plane centre is 13.643, adding 1.2 , gives 14.84, about 2 " lower than the dry frame? relative to the motor that is

never mind all that, I am sure it will all be fine, its been a popular upgrade for decades.

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod