About 3 years ago I bought a paperback book at the FE Race and Reunion titled “Thunderbolt” authored by Charles R Morris. This book pretty much echoes what has already been said that all Thunderbolts started life as a 289 Hi Performance K code before shipment to Dearborn Steel Tubing Company. The appendix of the book has a Ford Inter-office memo listing the first 8 serial numbers and who they were shipped to. These serial numbers are 4F41K118358, 59, 60, 61, 63, 66, 67, and 68. Note they skip over 4F41K118362, 64, and 65.
The 111 page book is a pretty interesting read covering pre-Thunderbolt Ford drag racing cars, the development and campaigning of the Thunderbolt and where it was headed after the Thunderbolt.