When you go to do the seals, do not turn the engine upside down with the rocker shaft off, the lifters can fall out and the are hard to get back in and must be put back in the same order as worn in, push rod must be kept in the same place also.
When taking off the rocker shaft be careful that the push rods does not stick to the rockers when you lift up or the lifters can get pulled out of its hole.
When putting the rocker shaft back on make sure that the pushrods are seated in the lifter cup and stay that way as you put it together, they can get out of place sometimes.