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Is there some trick for getting studs with rolled threads installed? I’ve been trying for hours and have so far managed only one. Maybe heating the block? I seem to recall reading something about them in the service counselor but can't find the entry now.

Don't believe there is any trick other than the cut and rolled threads are not compatible. The way I read the article which is on page 101 in this counselor, by the 23rd series all engines should have had rolled threads. I would wonder if at some point when Packard parts were not as readily available rolled thread studs were NA or hard to find and someone tapped the block to use the other studs. Does a regular stud or an ordinary bolt thread in? Out of curiosity what is the casting date of your block?

Good question about the casting date. A little hard to access (the car is so high, especially on the lift even when down to the floor) but I'll see if I can find it. It is, however, the engine that is original to this vehicle. If cut threads in the hole, I believe rolled threads should go in more easily rather than the other way around but I'll have to look up the specifications of cut vs rolled threads to be sure. In this case, someone likely did tap the block on some because these places where I am installing the studs had bolts, some of which were very difficult to remove.

It would probably take a cut thread stud without problems if it had a bolt before but one other question is are the hard to install studs definitely NOS rolled thread. I had heard from a machinist friend those threads are hard to do. At one time one of the vendors who was repro'ing studs when questioned as to type didn't know Packard used the rolled threads. They were just having two or three of the regular type studs made in various lengths as given in the parts book.

I'd try to jam two nuts together so the flats were aligned and then use an impact gun to see if that could break the stud loose. Vs straight rotational force on a stuck stud.

I used this trick to bust free stuck exhaust studs.

Howard, these are definitely rolled thread but whether NOS or reproduction I can’t say. The nut goes on easily on the non-rolled end but not on the other and, as these were done purposely with an interference fit, that’s expected. It occurred to me to get a rolled thread (tap) but they are not easy to find, especially here in this rural area. No time to order one either..

Kev, that’s what I am doing and it goes in but is still shy of the proper depth by 3/16” or so and that’s too much. Incidentally, I'm trying to install the studs, not remove them. To remove them again once I get them forced as far in as I can, I have a stud extractor

It almost sounds like you would be better off using a regular cut or standard thread stud and use some thread sealant at the block rather than trying to retap to a rolled thread. Even if you find a tap I would wonder how successful trying to rethread would be. Reforming the threads the first time would probably have done some damage and if tried again, the threads might further weaken to the point of not being able to hold the torque. If the threads were weakened and you had to use a heli-coil repair then I suspect the only option with that repair would be a standard thread stud.

Howard, I agree and, while I did find taps online, I don't really want to go that route anyway. I think before resorting to retapping, I'll try a little heat around the hole which might expand it enough. There are two holes that will require thread inserts from someone having put in 1/2-13 bolts and for those, the inserts are not rolled thread so I'll likely have to use a standard stud anyway.

For the drilling of the two enlarged holes, my brother made me a pair of drill and tap guides to be sure they are straight and perpendicular to the block.

The drill guide. The tap guide is similar but, of course, with a larger hole.

I'm sure you have, but have you compared the depth of the hole to the length of the stud to verify that they are just not bottoming out?

The studs typically go into the water passages below so shouldn't be possible to bottom out. I think that's in part why they went to rolled threads with an interference fit. A more likely scenario is tat there is crud down in the holes from having possibly shorter bolts in the holes rather than having studs.