thanks Robert
spoke to Logan on this one - the model without a gear box has, as you guys rightly pointed out, another bracket on the LH side (mirroring the RH end) with a support bracket for the lead screw...which would go the full length on such a model)
so just like the photo NGB posted (thanks for that!)
all beds got drilled for this
if a gear box was installed, it went on and covered these holes up
mystery solved
thanks again!