The stuck motor is from the pistons being stuck in the cylinders. OK, that's easy enough to figure out.

So how to get them unstuck? The only way I have ever been able to do it is a total tear down and then soaking the tops of the pistons with something like Liquid Wrench or an equal product. And this takes days.

Then, when they come loose, you just rebuild the entire engine.

But how can alloy pistons stick to an iron cylinder pot? Easy. Because it is the iron piston rings that are stuck, as in rusted together with the cylinder.

So throw in the price of an engine rebuild. And a 912 engine is not a 911 engine with two less cylinders since many internal parts are different.

Check out the price of cam followers and then know that you will need eight of them.

And since the cylinder bores will need boring you might also look into what a big bore cylinder/piston kit would cost. It might be cheaper than going with what you have after the machine shop is finished.

But it is all in the asking price. Consider what the repairs will cost, add 50% of that amount to your figures, and then roll that into your offer.