I installed the Richmond 6 speed with my 429. I had to knotch out a 6 inch long by about 3/4 inch wide space on the drivers side of the tunnel in order to clear the shifter linkage. I also had to redo my crossmember because the mount ended up a couple inces in back of the rear most mounts on the chassis. My driveshaft is still about 24" long so there aren't really any overall length issues. I went through and selected all of the ratios with somebody from Richmond. I can't remember all of the transmission ratios that we selected off the top of my head, but I have 3:50's in the rear.
Components are Lakewood bellhousing, Mcleod flywheel, clutch, pressure plate, and hydraulic throwout.
If your still interested I can try to dig up Richmond's ratio selection chart that I used and try to remember how we figured it all out (not my area of expertise).
There's probably no "real" advantage anywhere by using the 6 speed. However, it's different, more gears to shift, and it does raise some eyebrows now and then.
