You will need the area bolted down to be stiff and rigid, this is most easily accompplished by the addition of a wedge.
If you simply used a stack with no wedge, I expect you would have too much pressure on the stack in the area where the riser would end, creating a hinge there. Additionally, the holes drilled through the butt ends of your limbs may weaken them significantly given they are not appropriately beefed up in that area.
I would recommend you use a wedge...doesnt have to be a big thick wedge, but something at least .250 thick tapered down to a paper thin fade. They are generally about 8" long, but will depend on your bow design.