Couple 46rh questions

Truckie ,
Take a look at my build thread in members restorations

67/68/69 cuda dilemma

If you want to see how to fit one of these with stock floor shift. It's more than just hammer out the 3 spots in the tunnel you pointed out, although that is necessary. You will need to do that as well. Last 2 pages should be a wealth of info for you in regards to this. We are doing a 42RH with OEM floor shifter and console. The OD unit is the same as a 46RH. You will need to do about the same to get it to fit. With chassis level front to back 2° to 4° is the industry standard on engine trans angle. Mine was at 4° with carburetor base level. You will need to make your own unboltable crossmember as well. Stock wont fit.

Best of luck. My build thread is a roadmap for you to follow.

Matt