Guide to Regrinding Camshafts
According to Ken at Oregon, it's a no go on flat tappet to roller. Only half the flat tappet lobe runs underneath a roller. Some companies are doing it, but failures are high. On regrinds of stock LA hydraulic rollers, some profiles allow up to .320 lobe lift and others allow up to near .340 lobe lift. Hydraulic flat tappets can be reground into solid flat tappets, but most solid rollers are going to require a billet core due to spring pressures required in solid roller profiles.
Ken and I have talked at length about grinding me a solid roller from a stock slant 6 core. He said he really doesn't recommend it, BUT that if I kept lift in the mod .500 range so I could run a spring that wasn't too aggressive, it would probably be ok. He said he'd do it but of course it was my baby if something went wrong. Fair enough.
There's one of the guys on the slant6.org site that's had Ken grind him at least one like that and has had good luck with it. Race only, so no extended idle. So yes it can be done, Ken will do it, but be warned, since it's uncharted territory, it's all yours. lol
I'd also like to add that I've seen a lot of people say "you cannot change the camshaft LSA" but that's not true. The real answer is "it depends". I had Ken grind my 331 Hemi camshaft from a stock hydraulic to a small solid. He went from a 111 LSA to a 106. That's a huge jump. But, the camshaft looks a lot like a cheater cam from the 60s and 70s, as the base circle is almost even with the camshaft core. lol Ken said as long as I got correct length pushrods, which I did, It would work fine.
Ken has also told me that Chrysler cam cores are hardened way in, almost to the core, so re-heat treating is not necessary for them.
I have several stock slant 6 cores and am holding on to them. The last cam Ken ground for me, he wanted me to send in a core, but I paid the core charge and kept my core.