Single to double diaphragm booster on a 72

[chevy72blu]

I am replacing the brake booster on a 72 c20 with a 7" double diaphragm unit. The truck is disk front, drum rear, factory power. I have the larger 5" booster bracket.

I went with the double because it was all they had in stock. The salesman at Tucker's assured me that it is a bolt in unit with my original bracket and rod. However, I see many references being made to the small bracket with the double diaphragm booster. I'd like to know before pulling it apart much further... It looks like the threaded push rod is far too short. There are no markings on the booster, but it is gold anodized and I believe its made by CPP.