Octalink and ISIS both have smaller bearings to allow larger spindles while keeping the bearings inside the BB shell. If you are looking for more durable bottom brackets, I'd avoid either of those. Especially if the Meridian doesn't fit, then I think a new bike is probably in order. Can you get the 'dale seller to send you closeups of the cranks to try to tell what the design is?
I wonder if stepping all the way back in technology to something like the Davinci cranks with a phil wood bottom bracket might make sense as opposed to going to the newer external bottom bracket design?