All in all, the MBW looks like a nice modification candidate. Here are some thoughts/answers to your questions:
There is no doubt that the primary dilemna is the inaccurate BPH of the ETA movement. To mod the case to fit a 1575 movement, you would need to enlist the services of a very skilled individual (such as The Zigmeister). For the lug holes, as Ubi mentioned, the correct tools are needed. Once again, a fine fellow like The Zigmeister could do the job correctly.
I like the bezel width and the CGs on the (supposed) MBW. The overall 'feel' appears to be quite nice IMHO.
As far as the dial size... I am fairly certain that the dial is the same size as the 1675, 5512/3, 1680, 1665.
Like By-Tor mentioned, most aftermarket Tropic 116 crystals have 1.5x - 2x magnification, so your date issues could 'work out'. Remember that OEM T-116 mag is 2.5x
Overall, this is going to be a fun project!!
---> Please let us know how that caseback looks. Is it thicker than the 1675 and thinner than 1680/5513? This caseback issue has always driven me nuts. OEM 1655 sits very differently on the wrist than 1675 or 5513. I try on my aunt's 1655 every year when I see her in Tokyo and my daily watch for the past 15+ years has been OEM 1675. Mmmm...