Windsor pulley kits do vary by their combination of water pump and balancer. There are multiple lenght balancers and water pumps available as both factory replacements and universal aftermarket replacements.
We stock pulley kits for 2 combinations:
65-69 - 3 bolt balancer - RH inlet water pump - 3 7/8" (98.5MM) balancer mounting face to water pump flange
69-ON - 4 bolt balancer - LH inlet water pump - 3 1/4" (82.5MM) balancer mounting face to water pump flange
Most aftermarket balancers retain the length of the later 4 bolt balancer and can be fitted with both 3 and 4 bolt patterns
Late model EFI motors with reverse rotation water pumps will not accept standard rotation "early" or "late" pulley kits or bracket kits