Richard, the closest match to the block casting number is 1349046. According to the chart on Buicks.net, that covers 1961-65 401's.
The numbers on the front.....you are looking in the correct place. However, I generally see something like this:
On the right side of the motor would be stamped:
LR 368
LR= decodes as a 1965 Skylark GS 401
368= production code, or date it was built. We believe it's numbered as a 2 year cycle.....so 368 minus 364= 004, or built on January 4th, 1965.
On the left side of the motor, I would see something like
5B145586
Those 8 digits should match the last 8 digits of the cars VIN. The VIN plate is on a plate attached to the drivers side door jamb. The VIN doe NOT appear on the cowl data plate attached to the firewall.
In the example above, 5= 1965, and B= means the car was built in Baltimore.
The stamp used for a '6" often looked like a 'b".
Unfortunately, what you have stamped on your engine doesn't follow the normal layout.
It's most likely a 64-65 401, since the 63 and earlier engines used a different crankshaft for the old Dynaflow transmissions....unless of course, someone changed the crankshaft!
