Does the manual L77 have the DOD lifters? Obviously no AFM available. But are they still likely to fail?
The L77 is mechanically exactly the same auto to manual. In manual vehicles there is no provision for wiring to the AFM control solenoid and it's run as a V8 all the time.
The later L77's aren't as common for lifter failures as earlier L76's but it still does happen, particularly more often if the vehicle has been tuned and the rev limiter is increased as the heavier AFM lifters don't like to spin very fast (and the stock valvetrain is prone to valve float). Lifters can and do fail if you're lax on servicing as well as the internal oil passage in the lifters is very fine - if this gets blocked the roller tip of the lifter gets little to no lubrication.
Mine only had about 6,000km on it when the heads were lifted to replace them, an increased rev limit I think was the end of mine. I put a set of LS7 lifters in (all of the non AFM lifters supersede to the LS7 set when I checked in the Holden parts catalogue at the time) I got through the Holden spare part chain and an L98/LS3 valley plate with an aftermarket cam. I've done nearly 20,000km with the cam in and AFM delete with no issues, but I do change the engine oil every ~5,000km (which for me is yearly as I don't drive much in the way of distance).