Your Merlin was made before Merlin learned how to properly thread Ti so they bailed and used a pressed in bottom bracket like you are currently stuck with. I assume the taper is JIS since the original crank was a Dura Ace so fitting any Campy square taper crank (ISO taper) will be probematic at best.

You might contact Litespeed (Merlin is part of them now) and see if they can either thread or replace the bottom bracket shell and at what cost. I expect it won't be cheap. Funny thing is that Litespeed always supplied threaded bottom brackets, even in the time period your Merlin was built.