A-Body Console Shift Access Hole location
There is a round indention on the driver side of the trans tunnel where the floor shifter will go through to the trans for an automatic and I believe it is the same for the manual trans too.
Here are some pics of both an auto and manual trans locations. The 1st picture you can see the round indention I'm talking about where the shifter linkages go through the floor. This one is not cut out because it was a column shift car. The other 2 are the same car being converted to manual. One of the inside of the car and the other from under the car.
Photo credits to
@CrOoKs