I think all the ones in the USA were solid and passenger cars (Pontiacs) in Canada used hydraulic (so you could use either solid or hydraulic since they'd be drilled for the hydraulics). Part of the problem in using a hydraulic lifter in a 261 meant to use solids (aside from having no oil passage) is your camshaft was designed for solid lifters.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end