When my Dad gifted me my current boat, I had it towed from DE (non-title state) to CA, so I do have some tips:
When you bring to CA from out-of-state, make sure the trailer has a VIN# on it, DMV will "safety inspect" (really, "is it stolen inspect") the trailer and will look for it. My trailer did not have one (or more accurately, it had a partial VIN stamped on and a faded, illegible sticker), so I stamped a thin aluminum bar with the full VIN and riveted it to the trailer, CA DMV was OK with that.
Even in a non-title state, there WILL be some kind of paperwork / registration on the hull. If seller says "there is no paperwork in my state" he's lying. My boat had nothing but a small registration card from DE Fish & Game the size of a credit card, that and bill-of-sale was all CA DMV needed.
CA DMV does not care a whit about whatever motor is on it, no separate registration / title for motor in CA (I understand some states do that).