RE: Big Swamp Buggy ??'s
The brilliant part is the way the u-channels are mounted they are the lowest point on the sponsons and take most of the ice /rocks/sand hits - you will see in the pictures. Thea channels are of aluminum and are screwed and epoxied in place.
The way the plexi slides in from the back and and follows the curve of the rake on front it gets tight enough that no fastners are neccessary to hold it in place.
I think you are right to go with the .61 with the added weight of the above, it will scoot on water or ice or land.
attached is a pic of my motor stand.