I'm gonna go out on a limb here and say it was aftermarket, and here's why.
V8 Mustangs all had 140mph speedos, except for Cobras, which had 160mph ones. The SSP cars (all LX coupes) had factory 160mph speedos. I don't think Ford ever made a 180mph one.
IIRC, the 4-cylinder cars were 85mph, while the V6s were 120.
|