Welcome to the board!
As Jim says additional pictures would help. When I first saw the picture of the US90 several red flags popped up. The frame neck and front fork should be painted the same color. Granted other 90 pieces are missing but whats there could be used to make a rider. The rear axle/hubs present another problem with needed adapters and 3 bolt wheels. Depending on the actual condition of the front tire could be sold for a good profit. I say sell and buy a '75 or newer 3 wheeler.
"HJ"
’84 YT60
’85 350x (423cc) with ’81 XL500 head conversion
’83 XR500 (628cc) converted 3 Wheel hybrid
’73 CB750 K3 converted 3 Wheel hybrid
’86 TRX250R chassis XR650L engine hybrid
’89 TRX250R (stock )
’90 LT500 Quadzilla
’85 FL350 Odysses ( water cooled head )
Lost (sold) but not forgotten ’80 ATC 110 (205cc on alcohol ) ’83 200x ( 222cc ) ’83 200x ( 185s eng ) ’85 350x ( stock )
added to the collection recently, (2) '70 US90 Aquarius Blue and '74 ATC90 Daytona Orange