Chad gave some valuable feedback on the Facebook Page regarding the sizes of the PSRU seals, copy-paste below:
Note to everyone, the part number supplied by harold will not fit most of the psru’s. Harold has one of only about 5 or so psru’s that run on a single 8 in wide belt. The size of his seal is 105 OD, 70 ID, 10 thickness.
If you are running a psru with a dual belt system, you need yours to be 100/70/10 or 100/65/10. Can’t remember exactly, but the dimensions will be stated on the seal itself.