welcome! I am a huge fan of both the M-65 and hollow M-75 (Aristocrat and Bluesbird) and have a handful of vintage M-75s and a couple 1960’s M-65s. This response is long and probably too detailed (and probably incorrect in some areas!).
I will provide my thoughts on some key similarities and differences but be aware that vintage Guilds can have specification differences by year or even one-offs so take these as very broad general comments. If you compare the body shape, scale, and general construction technique between the M-75 and M-65 (not M-65-3/4) they are the same size with the general same type of construction technique. As such, they feel very similar when playing other than the M-65 being a little lighter due to one less pickup and less electronics. As you noted earlier, the M-65 has f-holes and this, along with one less pickup in the top, makes it sound (to me) a little different acoustically. To me the M-65 can have a louder and more full acoustic sound. Great couch guitar!
In my mind, I lump all fully hollow M-75’s into one broad category with a few different flavors (I am leaving out a ton of details but here are some general “standard” spec highlights):
1) Aristocrat 1954-1963: Mahogany back and sides with spruce top and Franz pickups.
2) Bluesbird 1967-1968ish: Same design and wood choice as the Aristocrat but with Guild Anti-hum pickups
3) Bluesbird 1968ish-1969: Maple laminated body and top with binding on the front and back with Guild Anti-hum pickups
4) Bluiesbird 1969-1972ish (Maybe some in 1973?): Laminated maple body with neck joining the body at the 18th fret vs 16th on previous versions. Anti-hums were the first pickup used then they transitioned to HB-1 pickups around late 1970-1971
The specs above are high-level, general, and do not always hold true. For example, I have a full mahogany body Aristocrat rather than a mahogany back and sides with a spruce top. The M-65 generally followed the body specs above (wood choice and neck joint to body location) but would have a maple top rather than spruce and you also see more full mahogany body M-65s. The M-65 trim was more simple than the M-75 (no block inlays, etc.). The pickup option started off the same as the Aristocrat with the Franz pickup but after that they did not follow the pickup choice utilized in the M-75. They went to the Frequency Tested chrome P-90 looking pickups around 1963 and then around 1965 transitioned to the Mickey Mouse single coil pickups. I have not seen an M-65 with a factory Anti-Hum or HB-1 pickup but you never know with guild. Now that I made that statement I am sure somebody will post a photo of one!
If you want an M-65 closer to an Aristocrat then the first generation M-65 with the Franz I feel is the closest. However, I really love the 1963-1965 M-65 with the chrome P-90 looking pickup. I have one and it is a keeper. You can also find these older M-65s with bound necks and Guild inlay in the headstock or even the chesterfield inlay compared to the later versions with the silkscreened Guild logo.
good luck on your hunt for an M-75 or M-65! As others have noted, a reissue NS Aristocrat is a great option unless you have your heart set on vintage
), and it plays and sounds great. The late '60s M-65s are well made, too, but the silkscreened logo and less refined look make them a little less appealing to me.
