I have a 49 PU with original 216 which I only drive once every month or so. When I tried to start it a few days ago it first made a loud clanking noise then a popping noise but it did start and the noise went away. The next day I only got the popping noise but it would not start. I checked the compression and on cylinders 1-4 it ranged from 60 to 90; however, on cylinders 5 and 6 I had zero compression. I removed the oil pan and valve cover and saw no obvious problems. Any suggestions as to what to look for before I go further. I had the heads reworked about five years ago and at that time I replaced the rings.
Thanks. JD
