I've had a problem with the engine missing while on tick over which would clear when revved up. I'm thinking now that being this is a 1968 engine which has adjustable hydraulic lifters, which could possible be the original ones, in which case if any of these were failing while on tick over this could possibly be my problem. I've decided to replace them, would it be advisable to just replace the lifters and keep as adjustable ones or would you suggest replacing the studs with lock down studs which would eliminate to having to adjust them in the future. Would there have to be any other alterations. Appreciate any suggestions of the best route to take.