Value of 3.0L Engine?

I'm trying to get an idea what the engine in my '78 911 is worth. The top end was rebuilt approximately 80k miles ago, and it has all of the updates, such as Carrera tensioners, Turbo valve covers, etc.

Thanks!

Stock SC motors are going for around $3500 in my area. Updates for a 20 year old motor are expected, so subtract if missing. A nice (read SSI) exhuast would increase the value.