How can I replace an oversized Chater-Lea bottom bracket with cotterless cranks? I'm building a tandem at the moment. The frame appears to be threaded for a 1.45&quot; Chater Lea bottom bracket.
I'd like to fit a modern bottom bracket. Any ideas? Here's my ideas so far:

Threadless cartridge bottom bracket: Shell ID is probably way too big for these, but maybe make a sleeve to go inside? Will that give enough grip?

Machine a counter bore for press fit bearings: Doesn't leave a lot of material left on the BB.

Drill the ID of the cups to accept a JIS spindle: No idea how I'd calculate what size balls to use. Also cups are really hard so difficult to machine?


EDIT:
I should clarify, the question in hand is about the rear BB, which has a shell width of 74.5mm. Chain tension is not an issue, since the front BB is eccentric and I'm sure I've got a solution for that.
You can just buy Phil Wood bottom brackets for Chater Lea.