I went thru this same thing years ago. I have a 51,235 with hydralic lifters (Auto Car). I had a valve job done and threw the head back on. I trusted the shop and shouldn't have. The thing was nosier than all get out. After weeks of adjusting, hot,cold, changing the lifters and everything else I finally spotted it. The shop had placed the valve spring keepers in the wrong (lower) slot. I put the keepers in the proper (upper) slots and it ran quiet as it should.
