It's easy to over-think this. It's more important to use assembly lube on new parts that need bedding in, IMO. If you're re-using parts that are already mated to each other it's perhaps not so critical to use assembly lube.
Even if you just use engine oil and don't start it for a couple of months later, that's surely no different from starting an over-wintered bike after a while? How many people panic about starting their bike after a winter lay-off? The main difference I suppose is that the oilways will be 'primed' to an extent and theoretically the top end will be lubricated more quickly than if it were a freshly buttoned up motor.
But I tend to hedge my bets. If I know it's going to sit for a while, new parts or not, I'll use assembly lube around all the 'metal to metal' areas and seals. It just gives a bit more protection against wear until the oil reaches where it should.
