c4 with 2.80's

[66StangGuy]

I was wondering if anyone can confirm this.

66 mustang 2.80 ring and pinion. stock c4.

with 2.80's and 3rd gear in a c4 is 1:1 ratio. with this combo my top speed would be 166 mph. My friend said that that wouldnt sell anyone this combo back then so what they did was they would change the third gear to a lower ratio so it would lower your top speed. i was wondering this because with my old 2.80's at 5,000rpm im at about 85. i was planning on going with 3.73 and didnt want to lower my top speed any more then that. i still want to drive freeway. so if this makes any sense to anyone please let me know. if i gave you numbers off the c4 could that tell you anything and if so where are they located?