I'm afraid those numbers seem a little screwy. May I assume the tag looks more like this?:

390    66    6     5-J    357  8

This represents a 390 "Z"-code engine of change level #8. It was assembled at the Dearborn Engines & Foundry plant in September, 1965, for use during the 1966 model year. Basic engine ID #357 appears to have been specific to the Thunderbird car line, always mated with either a C/M or C-6 automatic.

To learn more, please visit our "Obsolete Engines Textbook". You can click that link, or use the ENGINES button found on every page of this Forum. Hope this helps.  :-)

Mr F