The Ford parts book does cross reference the I.D. # on the dipstick for many, but not all applications, and in this case I don't see your dipstick I.D. Listed in my version of the parts book. Both C4's & C6's use the same 9/16" dipstick tube diameter so the fact that it fits doesn't necessarily mean it came from a C6. It be from either a small block or a 400/460. Sorry I couldn't be more help, maybe someone else has the answer.
