I would say, mount it to the ground. Make sure that left side where you check loft/lie is Dead flat using a digital angle finder. if not you're going to have incorrect lie readings and will require mucking about with two angle finders and a razor blade to get the correct lie from the club sitting dead flat on a non-flat surface, like I have to deal with here
Enjoy it and have fun! practice bending and measuring a couple clubs until you get it right. there's some "feel" involved with using these. Mine is a vise mount machine and it's been great, i dont do a lot of bending but its good to have the ability to do so. your rig there is good enough for you to do it for others and charge for the service.
IMO the purpose of bending is to find the ideal hand position(relative to the ground) and to duplicate that position for every club. ie exact degree of lie angle doesnt mean anything, as long as every club is same height from the ground.
14:12, "club design has butt of the clubs the same distance from the ground"..George Knudson