Saw this on Ebay today.
https://www.ebay.com/itm/1968-SHELBY-MUSTANG-GT500-4-SPEED-428-PI-ENGINE-FROM-SHELBY-00801-ENGINE-ONLY/292550399698?hash=item441d5cd6d2:g:9GQAAOSwRdta7QOL&vxp=mtr
reading the 69 GT350 description and they put 68K on it in 4.5 years. Well driven.