[Andrew Rowe]

When I have rebuilt Valentines, with the 671, you can indeed upgrade the injectors to the later "N" - series to increase the horsepower to 190 to 200.
This still uses the original 6004 engine block and 2-valve head and original governor, but you also do a change of the piston liners to the latter "slotted" version with a 17:1 compression ratio.
I would also state that it is entirely possible without too much problem to change out an AEC engine for a 671. The front engine and gearbox mount holes are identical, the only real difference in the engine compartment is the 2-lugs welded on the side for the oil cooler in front of the radiators and the main water pipe to the engine water pump is on a different side. Steering clutches and everything else will just line up.
There would be a couple of extra throttle linkage brackets to change and the gearbox gate shifter housing would have to be changed over as well, but all controls front to back remain the same, Cheers Andrew.