As crude oil is a mixture of all sorts of hydrocarbons, it doesn't have a single molecular weight. API gravity is just a measure of the of the relative density of the fluid.
°API = (141.5/ Fluid SG) - 131.5
So a API 43 crude will have an SG of 141.5/(43 + 131.5) = 0.81.
So it's a pretty light crude oil, so I'd guess quite a lot C4- C10, not much waxes.
You can estimate the Watson factor if you know something about the crude, i.e. is it paraffinic or asphaltic. There are some charts in the Campbell Vol. 1 book that tells how to do this.