289 hp?

A stock 1966 289 has 225 hp right?

some did
"A code" had high compression producing 225 instead of the lower 200hp and 210hp models

C code 289 2 bbl=200 hp at 4400 rpms.
A code 289 4 bbl=225 hp at 4800 rpms.
K code 289 4 bbl HIPO=271 hp at 6000 rpms.

D code low compression = 210 HP
Shelby HIPO + high rise aluminum intake, 715 CFM Holley, and Headers = 306 HP

T code 200CID 6 cyl 1bbl, 120 hp at 4400 rpms.

As far as I'm aware, there was not a D code for the 66 model year.

Also just want to point out, that there were two different K code 289's. One as a option in the Mustang, and the other in the Shelby. The Mustang was the 271 hp version. The Shelby had two different ratings depending on tranny. Auto's had a 595 cfm Ford 4 bbl, standard's had the Holley 4 bbl.

i hear that the G code ran on gerbles lol jk.. i like older stangs i wouldn't mind owning a shelby 350.