Neff,
Your posting has been here for a while so I assume you have not sold your Comanche. Engine time is a limiting factor.
In a similar, current sale situation we purchased a lower time engine from Wentworth to make the airplane salable. The price of the 500 hour replacement engine was $13K, and the old engine has a $5K (rebuildable) core value. Net price of the engine exchange was then encorporated in the sales price.