[Mgs] What year and B engine series

[W. David Houser]

Listers,
Got a rescued B engine that I am rebuilding. Don't know what year car  
it came from. It's a 68> as it doesn't match my 67 BGT engine. No  
carbs came with it. No intake manifold. No engine plate numbers on  
head. Engine number on side is 12H3248. No dipstick. Some clues: Head  
on it says 12H2389, AFI. Date stamp on head says 4-21-70 in a circle.  
( Has it been swapped a some point? No idea) Also, it has blocked air  
injection ports, of course. Water pump has a bracket that might have  
attached air pump. Looks like item # 13 P. 16 in Moss catalog. There  
is a bracket on the side of the block by the distributor that holds a  
round oil pressure switch? Valve cover has a vent valve on rear that  
was smashed but looks like it went to the side not back. MG decal  
only. Inverted oil canister. Flywheel/Ring gear measures 12.75  
overall, flywheel is 11.5. Dipstick shape is 3-1/4" and from what I  
gather from www.mgamgb.com is found on all 18GF, GH, GK engines only.  
So what am I?
Let me know if you need more info.
Cheers,
Dave Houser