</font><font color="blue" class="small">(
Although some of the 4 cylinders suffered from porous engine blocks but i'm not sure if it was a problem with these , Fords Replacement blocks later on had ribbed pattern on them these were good , )</font>
The 4600 was (is) a 3-cylinder same as later model 4000's. Nary a problem with this engine. It's what makes the 4000/4600 so great. Torque galore.
I'm not "up" on David Browns, but some models had a better reputation than others. Some were good tractors. Some were money pits.
My "book", an old apraisal guide from 1994 says "SU" is "special utility".