i've done some testing with these vacuum pads up to 50mm, they will work fine for engraving or fine cuts however due to the tiny footprint of the stiff o-rings the friction is a little low and there is the risk of the part slipping latteraly

jonathan, i've sent you a couple of syringes some tube (i found some more) and a one way valve, the valve is a medical job and it takes quite a bit of pressure before the seal is broken and it allows any flow so it needs to be mounted on the tip of the syringe to reduce pressure backlash, not perfect but it will give you something to experiment with, i'm leaning towards your idea of making a bolt down board unless i can find better seals, car oil filter seals might be much better for individual pads, they have a square section and a much larger contact area

i've sent it to your uni address