Magnuson doesn't advertise the kits. You must call Magnuson Products and ask their remanufacturing department staff for the kit. And yes, they will sell you a coupler...at least they used to - I bought a kit from them over a year ago. They call one of the kits the "moly guard" kit and it costs $25. It includes the coupler, sealant for the nose mating surface, a new drain plug, a bottle of supercharger oil, and an instruction sheet. Or you can get the nose oil seal with the kit also, for $30 more. I don't think you'll find this seal anywhere else; I wasnt' able to. The OEM seal has a teflon lip with sprial grooves on the lip.
The nose bearings are 6203.c3 and 6204.c3. NSK and several other manufacturers make them.
To check for causes of noise at idle, also check the pulleys, belt tensioners, balancer, water pump, and alternator too. Listen while the engine is running and use a mechanic'* stethoscope or a rubber hose next to your ear.
'99 Bonneville SLE, white, 112,000 miles
'02 Park Avenue Ultra, white diamond pearl, 88,000 miles