The VR57 is a totally different design blower than the SN or VS series blowers, The VR57 has larger diameter balls than a SN/VS and was a variable ratio(VR) as well. No SN/VS parts are interchangeable with an original VR57.
The original VR57 rear seal is the major flaw. The original design used blower boost pressure to block oil from coming out behind the impeller. If the blower belt is off or the blower is not making pressure, oil is sucked around the output shaft seal and into the intake track by engine vacuum. The car cannot be driven with a non-functioning VR57 blower.
The original VR57 was inherently an unreliable blower and Ford/Paxton had tons of issues with them. That is why Paxton went to fixed ratio VS/SN type blowers after that.
Currently, the most common thing to do to a VR57 blower is to have it converted to SN internals. SN balls, races, seals, output shafts, and ball drivers are still available brand new. The leaky original design rear seal is retrofitted to the modern SN seal by boring the housing to insert the modern type SN seal. Then the SN size output shaft can be used. Race adapters are manufactured and pressed into your original case to hold the smaller size SN races and balls are now used. A new custom designed conversion input shaft is made to hold the modern SN bronze ball driver. The drive mechanism is now all modern parts that can be replaced if ever necessary The converted blower will no longer a variable ratio blower, but a fixed ratio, which is more consistent and reliable. The converted blower uses a special Beeville Washer/Spring to put pressure on the balls and races. That determined tension is set to a certain rotational force using shims to create the proper tension so the balls don't slip when the boost/rpm goes up, but not to much tension, as to create excessive wear/heat.
A converted blower looks exactly the same on the exterior, but the internals are now modern and the car can be driven regularly again. Also the car can now be driven with the blower belts off, as the modern rear seal prevents any oil seepage.
The conversion is an investment. The conversion parts are custom made, specialized, very precise, limited supply, and pain to have manufactured. You add the cost for the brand new Paxton SN internal parts, and the labor for the time consuming conversion along with testing there is an expense, but you have a modern working and reliable supercharger.
The conversion design was created and refined thanks to several of the senior members of this forum sharing their knowledge and hard work to keep VR57's working on '57 Fords and T-Birds.
Pat Fleischman