OK, to muddy the waters even further ...... I recently rebuilt an engine out of a QL, the block was not machined for the filter. So it was made specifically for a QL. Main bearing was different in the thrust location, no flanged shell as block was machined for the commonly used half round thrusts, one with a tag, other plain. Also big end diameter was smaller. Casting date on block put it at mid-1950's, 10 years after the last QL was built.
The engine was in fact the Extra Duty type that was introduced to civilian models in early 1950's. As it was still on standard bores and going on other things, I deduce this was a new engine produced by Bedford for the Ministry of Supply under contract and they used the latest version of the 28hp. Around the same time a friend was rebuilding a MW engine (it had MW prefix on its number) and asked me why it had separate thrust rings, so not an uncommon occurrence. With all the rebuilding of WW2 vehicles going on at the time with the army, parts were still being produced to keep them running.
Oh, and reason the big end diameter was smaller was that the bearing shell materials were improved.
cheers Richard