I put the Richmond 6-speed in my '66 but it is not a big block car. I used the stock drive shaft and transmission mount, but had to make a new mount bracket. The midyear trans mount bracket is not the same as the '68 and later brackets. You can use the original bracket mounting points, so you don't have to modify the frame crossmember at all. It's pretty easy to make a new bracket out of 1/8" steel plate with minor welding. I can send you my drawing if you want it. The rubber mount itself works fine if you trim the corners off a little for clearance. The drive shaft is O.K. except for changing the front yoke to match the Richmond output splines.
The console required about a 1/2 X 1" piece to be removed from the trans tunnel and the console itself at the left rear corner where the stock unit tapers in toward the center line. I bought an old console to cut up and saved my original one.
The shifter is a tight fit in the opening and required some persuasion and minor trimming of the tunnel to get it in. Also, the reverse gear shift arm interferes with the tunnel and I had to cut a relief hole in the side of the tunnel which I covered with a wedge-shaped piece of sheet metal screwed over the opening. It's alongside the seat and doesn't show.
I used the stock pressure plate but had to change to the 26(?) spline clutch disc.
The speedometer cable works allright but it is a challenge to install it -- very tight clearance to the tunnel.
All in all the job was more work than I expected but that almost always seems to be the case, doesn't it? I am very happy with the way the car performs with this set up, but I should warn you that the Richmond trans is noisy and the shifter is stiff -- i.e., I can't flat shift from 2nd to 3rd or 4th to 5th. I am using the stock 3.08 rear and that ratio is very good for the street with the low (3.27) first gear of the trans.
If you have any other questions just ask. Have fun!