I got a hold of a 1988 Suzuki rm80 triple tree bracket for measurements. Looks like this one:
Made of cast aluminum, it's weighs 3.2lbs, heavier than a DS80 tree.
It also has a 1" steerer tube and is 1" shorter than the DS80 steerer tube. That means no cutting/rethreading and less shimming. The beauty of this model is that it comes with a factory motorcycle disc brake!
This triple tree accepts 33mm fork legs, compared to the DS80's 26mm legs., so fork travel should be less. It also has adjustable top and bottom clamps, which means that the fork tubes don't have to be opened when you remove the tree top or make adjustments. No oily mess!
The Suzuki RM80 uses a 17" wheel. To run a 26" tire, one needs to respoke the hub to a larger rim. However, the RM125/RM250 uses a 26" tire. I'm gonna look for that triple tree bracket. If it has a 1" steerer tube and fits onto my bike, I'll consider that one. Since the RM125 has 35mm fork tubes, fork travel will be even less. It also has adjustable top and bottom triple tree clamps, so no messy oil spills too. If it fits and isn't too heavy, I'll use the RM125 and factory 26" tire.
I got to see an RM125 triple tree bracket.
It is HUGE and weighs 5.6lbs! the steerer tube looks to be a tad over 1". It MIGHT fit my headset. However, I believe its size is not proportional to a bicycle.
RM125 tube WILL slip into a 1" headset. However, the shaft's bottom is tapered to a larger diameter to accept a bigger cone-style bearing. You'd have to machine the tube to accept a standard 1" bottom bearing race, then shorten and rethread the shaft. Too much trouble and expense.
And I haven't even seen the 35mm fork tubes, which are larger than the 33mm RM80s. All this adds more weight, so I'll stick with installing an RM80 fork with motorcycle disc brake.
RM80s have a 17" front tire, RM125s have 26" tire. With the right axle and bearings, maybe the large wheel will fit in the smaller fork.
YAY! RM80 triple tree fits an early cruiser frame like a glove!
It simply needs 38 ball bearings, 19 up/19 below the headset to match your standard cups. Balls are 3/16" size. I'm using the motorcycle's bottom bearing race and its top bearing retainer. Cost is less than $4. Upper bearing retainer must be reamed a fraction of a millimeter to clear the tube's machined shoulder. Instead of rethreading the steerer tube, a few large washers above the retainer will permit the ball bearings to be adjusted. The handlebar clamps are 7/8" and massive; no fear of cracking, and the standard bike handlebar should bolt on with no reaming. Then the RM80's brake lever should bolt onto my motorized bicycle.
Now I can start hunting for wheels, RM80 forks, axle and its entire front hydraulic brake system.
The first wheel I'll get is the RM125 26" one with disc rotor. Maybe an RM80 axle and bearings will slip onto the wheel.
And maybe the larger wheel's rotor will match the smaller fork's caliper. If that happens, I'm a happy camper. If the larger wheel won't fit, then I'll find
two RM80 17" wheels, one to run as is. The second one is to respoke its hub to the RM125's rim.
If I'm lucky there, the larger wheel's spokes can be re-used.
More researching needed.