i think you're right on both counts George - 20mm and looks like a very nice small hole corfam - this is unusual for a monza, as is the signed crown.
AndyO...

: To me that band that's on the watch is a Corfam Strap from the
: 1970s, it also has the original Heuer Sun Buckle... Those can be
: found at a premium. I'm not sure what's the lug width of this
: watch. I know I've seen the Corfam Straps in 20mm and 22mm,
: occassionally there are 21mm ones also. If I took a guess it may
: be 20mm that this watch needs. Experts on the forum may be able
: to tell you more...

: ~George