That's a nice find for your buddy. The blue model was known as the "Christmas Special", I believe any '81-85 year ATC70 cover will work. Question for you, does the rear fender still have the original decal, been looking for picture to have new ones made?
"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