235 question

[Chris.]

so I have a 50 3100 that I slowly learned (as I learned more about these trucks) that some body did a lot of changing such as the fact that it has vent window doors and that it used to be blue not brown and the guy I bought it from had a title since 1984 that said brown so it must have been the guy before him. anyway I did some looking today and found as many castings on this engine as I could

Block = 3769716 that I found is a 58-62 235

Head = 3836848 that I found is correct for block

Prefix/suffix = F0309A I found that meant produced in Flint, and that it was made on March 9th, and I think A means stand model engine?

How can I determine the year?

Finally I found this on the head above the Block# B57 848 850 haven't been able to find out what it means

The other part of this question is; is this a good engine to start off with for a mild performance rebuild?

Thanks for any info,
Chris