Here's a couple of graphs of advance curves for some late '60s to mid '70s Alfas that were fitted with Bosch distributors in the Euro versions (the 041 and 044 in particular although an 045 was also used but I have no curve for it) and Marellis in the US. The difference in the curves is astounding.
I would think that a dist specialist or a hotrod shop could recurve your Marelli to the Bosch specs without much trouble. Or, as you say, just get a Euro Bosch dist. Although 'un-tampered with' Bosch units are out there, the 30 or so year old springs inside could be somewhat ummm....fatigued - as well as the bushings.