I am looking for a concise description of the APR tolerances under Reg. Z?

There is a pretty detailed article in the ABA Compliance Magizine from March/April 1998 titled "Compliance Alert: Restitution Redux: The Tila Reimbursement Rules After The Rodash Amendments". It is written by by Alan J. Dombrow, CRCM, and Walter E. Zalenski.

Since you probably would not have that unless you have way too much storgage space, or access to a regulatory service, you might go to the FDIC-Compliance Examination Manual Appendix E -- Truth In Lending Reimbursement. While not as "fun" to read, it is pretty detailed.

There is an earlier article in ABA Bank Compliance by Alan Dombrow from 1996 or 1997 that had a flow chart on the last page of the issue showing the TILA finance charge tolerances. I remember this one because I co-authored the "More Alligators in Swamp" article in that issue.

Don't forget to factor in the TIL enforcement policy tolerances.

Here is the link to the OCC TIL Handbook which talks not only about tolerances, but about restitution.
http://www.occ.treas.gov/handbook/til.pdf

There is also a detailed discussion of it in the Commentary for section 226.22.