I know the 77/8 F bikes had the valve guide issue but the valve guides in the 77/8K and earlier F bikes are the same as the earlier years at least according to the part numbers so why would they suffer any premature wear?
You have bikes like Ofreen's F with 140,000+ on it without valve guide problems and then the above post that need replacing at 24K. I am inclined to say if you like the bike and it checks out fine then just get it and don't worry about it. We could probably pick any year and pick it apart with "issues".
Sadly, while Honda's part numbers remained similar, they practice something called "delta changes" in their parts supply. This term means that if a [new] part can be fit into the engine/bike with no change to form/fit/function, but is less expensive to manufacture, it is implemented with nothing more than the last 3 digits of the part number being altered, in the middle digit. For example, if the part number is : [nnnnn-300-000] in the beginning, it would become [nnnnn-300-010] at the next "delta change". Thus, you can watch the evolution of their parts over the years, if you can find both old and new parts lists.
Happily, though: you can also 'see' the evidence of that change!
The 1975 and early 1976 F0/F1 engines had the nice stellite exhaust guides that came in the earlier K0-K6 engines, which lasted a very long time. Starting in the K4, the inlet valves became less-expensive steel. Starting in the K5, the valves (exhaust side) lost their stellite and became steel, which raised the wear quite a bit if the oils were too light (i.e., 10w-something oils). In the K7/8 and F2/3 engines, the guides became cast iron on steel valves, which wear quickly, regardless of oil. Add to that the extra heat of the F1 and later engines after the DOT made Honda the first 'example' of what happens if your bikes don't meet EPA emissions testing, and you get the late-cam, lean-burn versions we see that are so hard on their valve guides.
For the wise rider (in the 1970s era, that was...), switching immediately to the K&N air filter richened up the low RPM range a bit and really improved the engine's response and health, long term. I suspect this is what Ofreen did, but haven't asked him directly. This cooled the engines off immensely. If the mainjets were also raised by a 5 number (to 110), the post-1975 bikes fared far better in longevity, too.
For the most part, you can tell externally if the engine has cast-iron or stellite guides by looking at the carb types: the PD carb'd engines all have cast-iron guides. The only exception is the 1976 F1: approximately the first 4-5 months had (probably leftover) stellite, while the later ones had cast iron.
Stellite is expensive, and the 750 was facing stiff competition from Kawi and Suzy by 1974. Honda was trying to keep the costs and price down, to keep sales up.
In my [personal] Lifetime Analysis (which is based on our 40+ years of observation of the bikes), those bikes that used low-detergent, high-quality, 20w50 oil most (or all) of their lives have delivered VERY long life with little wear. Those that were mis-serviced by Honda's goofed-up mis-translation Jinglish of the post-1975 Owner's Manuals, using 10w40 oils of 'automotive grade', have become leaky at the rubber seals and have lost their valve guides, and often their cams, losing lift on the lobes.
