I tried to install on a 1999 Trek 820, but the down tube was way to wide. (45mm), and the Grubee Gen II fits up for a 35mm. So I tried the Sick Bike front engine mount, but it doesn't work with the Grubee Gen II either. (the Sick Bike mount is set for 1.6", between the stud centerlines. Where as the Gen II is near 2"). There was clearance on the 18" frame to fitup the engine, but the dang downtubes were way to large. And I wasn't planning to drill a center hole into an AL frame....
I punted, and found a 1990 Schwinn Cro-Moly framed MTB via Craigslist for $25.00. The down tube was 35mm, and the engine mounted up just fine.
just food for thought....