My brakes were bad. 1973 GTO 400, auto, no. 62 heads. I bought one of the all in one kits with booster, master cylinder, proportioning valve. I got the smaller booster for valve cover clearance. ( 9 inch.) Brakes work ok on first push, but no vacuum assist after. Really hard to stop at light. Do I have to add a vacuum can, or do I have to buy the 11 inch stock booster and replace the 9 inch booster. My bad brakes were better than this. Bled all the lines, new hoses in front. Thanks for your help.