[Aardvaark (R.I.P.)]

I spent time measuring rear window louvers on various cars at shows and discovered the 1969-1970 Mustang fastback louvers are very close to the Manta width wise and only a slight bit taller top to bottom. Also the rounded corners of the Mustang are on the top and not the bottom like the Manta. I can envision a bit of modding and they would fit the Manta pretty well. They are widely available new from Mustang sources but I don't want to spend the money to find out at this time.

FYI:
Manta rear window width is 42.25" outside to outside the moldings and 40" inside the moldings.
26"tall inside the moldings and 28" tall outside the moldings.

The 69-70 Mustang louvers I measured were 41.75" wide and 29" tall.
As I said. The tightly rounded corners are on the top instead of the bottom like the Manta.

http://www.lamustang.com/SQLCart/Images/Large/104385.jpg
Slightly different two piece construction and shape:
Mustang Rear Window Louvers Aluminum Fastback 1969-1970

http://www.mustangsunlimited.com/itemdy01.asp?T1=16000+01&Category=Exterior+Trim&CatKey=74-01

Astro-Hammond:
http://www.sfxperformance.com/parts/AST10555.htm

Food for thought.