north-shore
I would also say it appears to be a CJ motor. If you research the civilian Jeep websites, they may be able to help out with the approximate date of manufacture based on the serial number of the block. The M38 motors have many distinguishing features and none appear on your motor.
Maeserik
What was different about the supersonic head? This is the first one I have seen.
He'd have to go to the Kaiser/Frazier web site for that answer. The serial number is not a Willys serial. It's a Kaiser serial. Willys sold L134's to several other companies and just like Willys did the serials didn't go on the motors until it was determined which model chassis they were installed in.
The "Supersonic" is a Kaiser trademark ID'g the engine it was sitting on as a Kaiser Supersonic engine. Even though we know the engine was built by Willys and supplied to Kaiser by Willys. Willys did not install heads with the Kaiser trademark "Supersonic" on Willys jeeps. The engine serial is not a Willys serial number. To be a Willys serial it would need to be in one of the following formats:
3AXXXXXX for CJ3A or DJ3A
MCXXXXXX for M38
LRXXXXXX for a factory new replacement L134 engine
RMCXXXXXX for a factory new M38 replacement engine.
UXXXXXX for the Utility series.
TXXXXXX for the trucks.