The carriage bolt idea is great, wish I would have thought to ask before the entire thing was assembled. It's almost impossible to put in the pockets for the nuts now.
What about using something like a model #3379 end fastener and screw that to the LVL. Slide the 1530 onto them and tighten the screws down through access holes drilled through the 1530.
Or even a button head socket cap screw similar to the carriage bolt idea but tightened through a hole drilled in through the extrusion?