Looking for guidance. I recently rebuilt a FE350D AS27 in a CarryAll. The AS27 has adjustable rockers and tappets rather than hydraulic lifters. During the rebuild I discovered that the head was cracked. Replaced the head with one off of a AS11. See photo below. New rings, honed cylinder, lapped valves. I have run for just a few minutes. Upon starting it seemed to hesitate on the compression stroke. I am thinking that is is just a week starter. It ran and took it for a test drive. Drove for about 4 blocks. Shut it off to check everything over. All looked well. Stepped on the pedal it hiccuped and farted then nothing. Took it back to the shop and found that the flywheel key had sheared. Replaced the key and torqued the flywheel nut to 101 ftlb and put it together. Just started it up. Start up sounded normal. Drove 1.5 miles all sounded fairly normal. I did hear what I thought sounded like a little pre-ignition. Shut it off sat for about 5 minutes then started with a little hesitation on the compression stroke. Drove about .5 miles shut it off. Restarted no problem. Drove 2 blocks shut it off for 2 minutes and on restart it sheared the flywheel key. There is a small difference in the heads and the replacement (AS11) head is higher compression. Valves are set at .004 cold. looking for solutions.