Base trans was a 3-speed manual but not many like that were sold. Likewise, few buyers opted for the lowest price Powerglide 2-speed when they ordered an automatic on C2 (1963-1967) Corvettes.
But in any event, the top gear ratio on the 3-speed manual was nearly the same as the wide ratio 4-speed - roughly 1:1. (Neither were overdrive in top gear.)
The rear axle ratio makes more of a difference to top speed than the slight variations in top gear ratios of the transmissions on most cars of that era.
Roughly?