Crank bearing spacings
 

Just out of interest ( I want to understand the exhaust firing spacing ) Can anyone tell me the angular spacing between big end bearings ?
Also are 1 and 4 at the same angular position ? I assume so - same for 2 and 5, and 3 and 6 pairs ?

I just popped out to the garage and took a look at my crankshaft. I did not remove the crank from the bearing block to measure so this is by eye. Anyway, startng from the front of the engine, the rod journals appear to be in 180 degree pairs. Meaning the first and second journal are 180 off and so on. For the firrst pair, draw a line through their centers and stick that in your brain as the "1st pair line". The second pair are of course 180 off to each other, and the "2nd line pair looks about 30 degrees off the first pair line. The 3rd pair line appears to be 90 degrees off from the 1st pair line. Best I've got, perhaps someone has more.

crank spacing
 

Thanks for checking James
I have come to the conclusion that each pair must be spaced 60 degrees and 120 degrees to get even firing pulses