after a few trials, i will be using this cutting profile to bolt my 0.750" t-slotted spoilboard to the 0.500" wasteboard/base.
i am using countersunk (deep enough for 4-5 re-leveling/clean-up passes) 1/4"x20 plastic flange bolts and standard t-nut inserts from underneath (with pre-drilled holes for the spikes as not to split anything).