"4LR" engine number?

Our '63 Mk III Tux has an F-head engine with a "4FR" number above the water pump. When we first got it I did some searching on that number. The best answer I could find is that the 4FR number indicated a factory replacement block.

So, I'm assuming that a "4LR" number on a flat head means the same thing and that these engines were produced to serve as replacements for dealers or other installers.

Anyone have any other info on these engines?

 

Here is some info on the "4LR" engines.

http://www.thecj2apage.com/forums/engine-number-question_topic18135.html

 

4LR is definitely 4 cylinder L head Replacement motor, sold by Willys dealers to replace old worn out jeep motors.