M-20 decoding questions

[69rsss350]

It gets stranger and stranger...
Numbers on block pad behind alternator read...
VO418TDR
C 87178681
apparently not the original engine but how do these numbers decode and what do they mean?
Rear axle:
axle casting date is H59
The (BT) I mentioned earlier turn out not to be BT at all but part of the test numbers, I was looking in the wrong place.
The numbers on the passenger side front are difficult to read but appear to be:
C BM 082061. It does have 12 bolts on the cover, haven't been inside the differential.
The casting numbers on the drivers side are:
3969341 NF. These numbers are very clear.
These don't match up with anything I have found on CRG site except the date code. Can anyone decode these numbers for me and give me an insight into just what these all mean?