I know they stand out a lot. But I i have them bolted through the metal tray with bolts and locking nuts. I just wanted sound and now I have it! I'll look into making them invisible sometime. I like the look of carpet though, not sure how black headliner would look.
Spoken like someone from South Eastern Minnesota... If you were from Chicago, LA or NJ you wouldn't think like that... Man, I may have to move to Montana!
If you're lucky enough to have an un-mangled dash, especially in a '65-'66, I'd have to agree with your dad.
My '65's dash, however, went under the hacksaw several owners ago. I was going to weld in a patch panel, but since deciding to go more resto-mod with the car, I figure that I can put a DIN chassis head unit in there for a while and have some fun. In fact, I was thinking about an Alpine unit too - though I'd prefer green control lighting. I can always weld in the patch panel later.
For an undamaged dash, one of the Mustang-specific AM/FM/Cassette units work just fine - and if you want to play digital music files, check out a nifty contraption called a "Digisette", or one of the FM transmitter type .mp3 players that plug into the cigarette lighter.