Limited galley
oil feed before '68, so solids were the only option on most FE's. 1968 and up could run either hydraulic or solid.
BUT, the problem with solid rollers is the tiny roller bearings that support the roller wheel on the end of the lifter. How do you pressure feed
oil to those bearings? In the past, early rollers, there was no way, they relied on splash only. More modern rollers have a method to deliver pressure fed
oil to the roller bearings through the lifter itself. These new rollers are much more expensive than standard 'splash' fed rollers, but that may be changing as they become more readily available.