I am doing the same as you, (except my 71-72 valve is going on a 69 frame)
I haven't installed yet, but I purchased this bracket from inline tube. It is supposed to put the valve in the correct location, so you don't have to bend up your lines more than necessary. You CAN just bolt the valve directly to the frame, as many do, but that involves more line tweaking.
To me, it's worth the 22 bucks!
Part Number - BRK-04* 1971-72 GM A-body Valve Bracket *** $22.00*
1971-72 GM A- Body
Chevelle / Lemans / Cutlass / Skylark / El Camino / Grand Prix / Monte Carlo
Factory Disc Brakes
1964-72 GM A- Body
Chevelle / Lemans / Cutlass / Skylark / El Camino
Disc Brake Conversion
1971-72 A-body Disc Brake Bracket
This item is an exact reproduction of the 71-72 A-body disc brake bracket. All factory disc brake cars had this bracket to hold the prop. valve to the frame. Drum brake cars did not have this bracket only the front disc cars. If the car is being converted to disc brakes this item is a must to place the valve in the right location so the factory lines will bolt into the correct location. All the disc brake companies use the wrong bracket that mounts up by the master cylinder. All 68-72 A-body cars mount the valve at the frame. The valve will only mount correctly with the use of this bracket. This bracket will fit
This bracket may also be used if converting a 64-70 A-body to disc brakes using the GM 5 port valve. Although not correct, since 64-66 cars were not available with disc brakes and 67-70 used a two part valve one piece mounting on the frame and a second part at the master cylinder, this bracket does mount the valve in the proper location on the frame instead of up by the master cylinder.