I've only used solid lifters.From what I'm told the hydraulics are troublesome.
Chilled iron milkbottle type go with steel cams,the hardenable iron lifters looking like typical more modern lifters go with cast cams.When in doubt,strike a file on the side of the lifter,chilled iron are soft on the side,hardenable iron is hard.
The 1970 GM master parts manual lists only one distributor gear from 1938 to 1962....doesn't seem right.....


70 Triumph 650 cc ECTA current record holder