Ok, first, the glow plug system is 12V, the glow plugs are reated for only 6, that means they are red hot very quick. The beru/motorcraft will survive a lot of abuse. When I had jumped timing I had to glow 10-15 seconds to get the thing to start, and always had to use them, hot or cold. That said, I'd say for maximum tolerance of abuse the 12V glow plugs are probably the better choice. You could probably leave them on a couple minutes if need be. They do heat up S-L-O-W the application you want for that is the AC Delco from the early 78-80 5.7 diesel, they have the same thread and pitch as the 6.9/7.3. This was called the slow glow system, it's what my grandfather had in his Delta 88 with the 5.7 diesel, never knew it not to start but as a little kid used to gassers I thought it took FOREVER to cycle. This was no Wisco winter though this was NC, no -30s but 10-20* was common. The only drawback on the 12V plugs is they are more expensive than the ZD-1A berus. Unless you know a place to get AC parts cheap. When Paul still ran Diesel Auto Services, which back in the day when most of us were members of another diesel site was considered one of the better online vendors. He sold "Lucas Constant Duty Marine" glow plugs. A member figured out they were actually a 12V AC Delco glow plug but what application we were never sure, and Paul would never tell. I personally suspect that they were from the 5.7, other people thought maybe some Volvo marine application. I would buy 1 and glow test it and see if it performs to your liking. As far as oils synthetic would be better but it might be dicey to dump it straight in to an old engine like that without either going through something like a slow treatment(auto-rx) and/or changing out engine seals. If it was a fresh build or had already had been treated, I'd say something like Amsoil 5w-40 or Roteall 5W-40, since you probably should stick with mineral based for now, 10W-30 that is diesel rated from Shell-Rotella, Mobil-Delvac, or Chevron-Delo would probably be your best bet.... I've heard of some far north members using 0w-40 IDK if it was synthetic or mineral, I do know I have never seen an oil like that down here, especially not diesel rated, but here I have gotten away with SAE30 rotella in the winter(normally 15/40) and we think it is bitterly cold if it gets under 32* for any length of time at night.
