Are rod end dimensions relatively standard? I'm looking for some 1/2" bore 5/8" shaft rod ends which are relatively common, but I need the threaded shaft to be slightly longer than those available from Mcgill or Rally Design. Am I unlikely to find any?

Go to: aurorabearing.com

Plenty of detailed dimensional information.

Remember you can get top hat converters that convert 5/8 bore to 1/2 bore. Advantage is the angular movement is nearly doubled which reduces the chance of binding.

If you want a longer threaded portion bear in mind the shear load increases in direct proportion to the length of unsupported rod. There is a chance it would break that's why the standard sizes have evolved

Cheers