Re: 1987 Starcraft Magnum 150 Manual
I highly doubt you'd find a manual for the boat. At least nothing more than a basic owners manual, which is likely more in line with basic safety stuff and docking procedures than actual helpful info about your boat. Because every boat ends up being rigged differently with gauges, accessories, engines, etc. there isn't a specific manual for most boats.
If you need a manual for the motor, you'd have to get the model number and get one specific to your engine.
Might find more information on specs by tracking down a sales brochure for your boat. I found mine via eBay...