I would say that it depends on if you're looking for an engine you can drop in and go, or if you're looking for a base to rebuild off of...
I went super cheap knowing that I wanted it completely rebuilt before I used it. The benefit to a fresh rebuild is that you know what you've got then...ethanol safe parts, gaskets, etc, etc.
If you buy a 20 year old engine and drop it in, you've got a 20 year old engine...so I chose to buy cheap and get it rebuilt so I knew what I had. For me, that was a wise decision (since I don't have the knowledge to do it myslef)...for $1500, I should have a trouble free powerplant for the next 20 years. It truly was a drop in, turn key solution.
Lets say you paid $400 for that KC boat...you have absolutely everything you need to go forward.
There will be other boats absolutely true...but even the Alpha drive at $400 is a bargain...provided its good.
See if you agree with my math:
Runnning Donor KC Donor (as an example only)
$1200? $400 -Initial Cost
$ -0- $1500 -Rebuild Cost
$1200 $1900 -Intial "On the Water" Total Cost
2016 EPA Approves/Req's Ethanol Use in ALL motors:
$2000 $0 - Rebuild Motor for Ethanol retrofit in say 2020 or simply
because the engine is now 30 years old. Prices will
have also risen for the rebuild due to inflation & price increases.
$3200 $1900 - 10 Year Total Cost of Ownership
($1300) - $1300 downstream out of pocket expense
I guess that's how I looked at it with my engine rebuild...I'm trying to avoid the larger downstream expenses. Maybe Ethanol won't cause that huge of expense, but you still have an engine that's 30 years old...and will need a rebuild sooner rather than later.
Again, just my thoughts on the cheap donor vs. running donor.