I found this one and cannot identify which model this one is. The owner stated that it is an 18hp and thats all I have along with these pics:
Thats going to be one of the following models LD, LR, SL, or SR.
Its most likely to either be a SL1 or SR1, as you will notice the flywheel fan shroud is round the wrong way compared to what you would normally see, indicating that this engine runs counter-clockwise. The SL has rounded cylinder barrel fins, and the SR has almost square fins of a very fine pitch.
BHP is going to be in the region of 4 - 7 depending on model and speed settings.
You can confirm what model it is yourself by looking at the engine data plate (located on the injector pump inspection door), if this is missing, these details are also replicated on the flywheel.
The engine type will be contained in the serial number.