I second the pvc inserts if you do not have hutchinsons. TWF pvc inserts are high quality. hutchinsons are flexible and easier to get installed, but cost more.
I would run steel spacers if you can get them. Or just check the aluminum ones for torque often until you are comfortable with them.
I would use 12 to 16 oz of any quality tire beads if you can't get centramatics. The centramatics you need are $299 for the set.
most of the balance beads are going to cost from $80 to $150 for all 5 tires depending on brand you choose.
I would not try to recenter my own rims if you still know the person that did your custom 20's then I would take them there.
you can probably get the rims, tires, spacers and balancers for less than the cost of 5 name brand off road tires (35 to 37 inches tall) that would fit the stock cucv rims.