641/2 8 cylinder ????

Yes, the 260 V8 was optional, the straight 6 from the Falcon was standard. Depending on date of production, which is a great debate I am not going to step in to, the 289 V8, actually 2 versions of that 289 V8. A true 64½ regardless has a generator, not an alternator. Bottom line is Yes to your question, for sure the 260 V8 Windsor was optional. . For further reading, see http://www.mustangandfords.com/news/mustang-1964/

I have one with the 260, although they made several 289 that year also..The 260 V8, and the 170 I-6 was discontinued for the 65 model year, and the 289 was the only V8 you could order..... here's some quick facts,....Engine Code Engine Type [A]V8 289 CID 4V [C] V8 289 CID 2V [D] (64½ only) V8 289 CID 4V [F] (64½ only) V8 260 CID 2V [K] V8 289 CID 4V High Performance [T] I6 200 CID 1V [U] (64½ only) I6 170 CID 1V....hope this helps