There are two lengths of pushrods used on 54 and up engines, its the lifter that is different like you say.The 54 cam has smaller bearing journals than the 55-62 cams.I think the earlier engines used a longer push rods with solid lifters, but I'm not sure. If you have a set of 55 lifters and pushrods, go for it ,but its not good practice to mix and match used lifters.Wally, why do you want to use hydraulic lifters in a 235/261? Many guys report noise problems at cruising speeds.
