The Grande is the coupe body, that's why the glass is different.
Typically, most folks want the Mach 1, first, then a plain sportsroof, then convertible, then grande or coupe. Kind of a toss up on the last 2 since the body is the same, the grande just had more "dress" on it. typically the deluxe interior and a vinyl roof, chrome wheel well trim and several other pieces of trim, typically called an "appearance" package.
A Marti report is the key to actual production numbers and "rarity" of a particular build, as noted above about red Mach 1's with power windows.
I have a yellow Mach 1, 351 Cobra Jet, C6 loaded out with power windows.
I haven't seen another like it.
I also have a '73 Mach 1 with the 351 cleveland 2 barrel carb, c6 and it's pretty bare otherwise, but the Vin indicates it is a Mach 1.
Things were varied during the production of these cars, that's for sure.
i think low production numbers is not allways a good thing if its not popular in the first place....fast backs allways got more attention than grands...and i think it plays into the whole..grande was a lux car version..and the sportsroof was the renagade looking car...what kids remmeber the most..all that flash and fins and stripes...grande were usualy plain a bit....plus now days production numbers are broken down..out of the sportsroof mach 1's...only 6,568 come with the 351 4v and c6 trans...and out of the red ones..only 4 had powerwindows..lol....i think alot more orders driven the production of the sportsroof over the grande....i would run the numbers..and if it turns out too be under 300 made like it i would restore it possibly...but if high numbers..i would do what ever you felt happy with.
you know we almost got a cheap grande for parts..was going to take the glass and everything..till we started to notice..the glass in a grande wont work in a sportsroof..lol..weird..we measured itfront glass and side windows...and it was a inch taller lol...and if you notice the sports roof has sharp corners on the top of the glass..were the grande has rounded corners...just thought it was odd that they made the grande roof taller..maybe for the lux part..lol