If you don't have enough large handscrews, you may want to make a couple deep reach clamps (shown in the last pic) first as the building of this jig requires the use of four or more deep reach clamps.
The scrap construction grade boards were slightly cupped and lots of clamping pressure were put just in case to keep the boards together while waiting for the glue to cure. Yes, fewer clamps could do the job but the spring clamps were kept in one bag and I just put them on as I emptied the bag.
Nice job on the jig… But I have to echo Micheal1's comment on the clamp extensions… I am going to make a few sets for myself anyway, but you really should post them… They look like they will be a very handy addition to anyones clamp rack. Thanx for sharing the post.