Hey Kurt,
I have a Richmond 5 speed behind the 300 in my '66 Special, it's real fun to drive..... immensely better than the 2 speed auto!
The 5 speed is the close ratio without overdrive, 3.26 first gear and 1:1 fifth.
With the 2.78 rear, it's a (2.78 * 3.26) = 9.06 ratio from a stop in first gear. Takes a bit of clutch slipping to get going but it's fine. Combo is good for 70-75 mph at a comfortable 2500 rpm.
Ideally, I'd like a little more gear off the line, and a 5th with an OD ratio for lower rpm's at 75-80 mph. But the Richmond was such a great deal at $1300 slightly used. It was also called the Doug Nash 4+1 in it's earlier days.
I added the 64 alum 4 bbl intake and dual exhaust to the 300. Runs nice!