Really no different than donating a car.
The burden of proof for the value is on
you at tax time. You need to find several other references for the sane make/model year and engine, or some kind of "blue book" value.
If you couldn't sell it for $1500, the IRS might say that is not worth $1500
P.S. I did the same on an old boat I could not get rid of, but didn't bother claiming anything. Years later, the engine and trailer were gone but the 30+ yr old 15 ft hull was still sitting in their back lot