Ah, well
then, my copy won't help you there. I can tell you how we cope with big loads on the rotisserie, it may help.
The arms are adjustable up and down. The lower the arms, the faster the outer layers brown and then burn. So, the more mass involved, the higher I raise the arms.
An aluminum foil 'tent' over the entire cooking surface makes for a very even and thorough baking, despite the spit being raised high enough to keep things from browning too fast.
You can now buy pop-up thermometers in a range of temperatures (Safeway in Wyoming carries them, so Safeway California should, too.) Shove one in, following directions.
The main thing to watch with these units is that the water not evaporate completely and the spit not be too low.
I bet others here can give you advice on the best marinades to keep things from drying out too fast, etc.