If you have a valve spring compressor you could change valves your self but so much more is needed . Heads should be carefully cleaned and inspected for cracks and other damage or wear , guides replaced and reemed, valve seats resurfaced , any reused valves resurfaced, head to cylinder seating area resurfaced, etc. Not stuff your likely to do your self and can all add up to probably well over $200 . I've even know of guy's that will never leave the original seats in bus heads because they are known for falling out , so add on even more $ if you do that . But once this is all done along with the cylinders honed and new rings and assuming the bottom end is good ,you should have a very nice running motor. Hope this helps and good luck.
