Hi all I need help please?

I have an On One Carbon 456 with a 73mm BB. I have recently bought an E13 LS1+ chain guide to run a single 36T ring up front.

When trying to fit it I cannot get the chain guide in close enough to the BB using E13’s BB adaptor screwed to the ISCG mounts, the closest I can get it still means I am about 2mm too short whn I put the cranks through.

The BB had a 2.5mm spacer on the drive side that I swapped out for the BB mounting plate, but I still can’t get it in far enough.

The STX cranks I have, also means the inner bolt holes rub on the chain device when it is in as far as I can get it.

Options the bike shop are telling me at the moment are potentially buying an MRP device that fits to the BB directly or a new set of cranks that are 83mm wide then packing out the BB to suit.

I don’t really want to do either for money’s sake, so any help would be much appreciated.

Cheers

Peter