Yep the Mustang did have a 390 in 69. It was the last year for it. Mine has the 428 CJ. I don't agree with those libs Tom and Ray about the 69 Mustang. Mine handles just fine. I still drive it every week and still get a smile on my face.
I had thought the 390ci had been dropped by 1969 but not so. In 1970 I spotted a used 69 Boss 429 Mustang on a car lot. The asking price was $2,995.00. It was a bargain but no way could I afford it at the time. The same year I found a 427 Cobra on a Exotic Sports Car lot in Memphis, price $12,500.00. Those were the good old days.
A little known fact was that you could bolt a 390ci into a 1957 or older Ford car. Another bolt-in was the large 430ci Lincoln, Edsel engines into the older Fords. You could run rings around the 283 Chevy guys. Heh!