Just to add to the confusion, or more accurately... add to what we *don't* know about B20 blocks, I just checked the two short blocks I have sitting next to the race car. We'll refer to them as "black" and "red", 'cuz that's what color they are! Since these both have racing history, probably with multiple chassis matings between birth and present, I can offer no history whatsoever as to when they were made or in what vehicle they were originally installed. Anyway....

- Black does *not* have "bridge" castings in the pushrod area of #1 & #4.
- Red *does* have the bridge castings.

- Neither block has any metric threads in any area.
- Both currently have 6 bolt cranks installed.
- Both have the "extra" oil orifice on the right side near the filter.
- If either of the blocks has a date "code", it is just that... a code. No numbers jump out at you as obvious dates.

Incidentally, Black is of exceptionally poor casting quality throughout... as a result, many cast numbers are illegible (see below).

Stamped numbers following the cast "49" on the upper left side:
Black - 8284 2580
Red - 8284 36791

Cast number a couple inches below "49" on upper left side:
Black - 1-1?????6 (might be 1-100896)
Red - 1000197

Cast number behind flywheel (numbers cast in reverse):
Black - B-1??:? (might be B-101:3)
Red - B-101:3

Cast number lower right side, closest to oil filter:
Black - RDG 3A
Red - TDG 12

Cast numbers lower right side, closest to mount:
Black - B J12
Red - B D19

No other discernible differences at this point, but neither have been completely disassembled.

And here's a quicky shot of the "bridge" casting: the #1 cylinder area is shown.

--
1971 142E ITB racer, 1973 1800ES, 2002 S60 T5