I take the mounting tabs off the belts and wrap them around the Roll Bar tube (more surface area for the Belt to pull against) Additionally I don't believe "Y" belts are accepted by the IHRA or NHRA

"SFI 16.1 - Shoulder harness: A belt assembly, one strap for each shoulder, intended to restrain movement of the upper torso and shoulder regions. It includes adjustment and mounting hardware. Optional cross strap can be used to hold the shoulder harnesses together and if the cross strap is in front of the driver it must be capable of being released in a single motion. A Y-type shoulder harness, i.e. both shoulder straps become a single strap with one attachment point, is not permitted. (Effective January 1, 2005)"