I'd call Penn Yan and ask them 1. how much a core engine is worth. 2. What they think of rebuilding an engine with 8,085 hours total time and how many times and how well it will rebuild. How's the mufflers? I did'nt see your wingtip dent as too bad. The crack and a few isolated spots of minor pitting? No big deal. Don't count on your old Garmin being worth much. Old model and lots of years in the heat. How's the landing gear, windows, paint, interior.....? Dumping cash into an engine soop-up STC sounds like a bad outlay. This is an outdoor plane and if the seller felt you out for 16K, that's steep.
The engine was a Lycoming rebuild installed in 1999 with 1900 total hours on it at the time. It's got another 2400-2500hrs on it now, making it around 4400hrs in total. A call to Penn Yang certainly wouldn't hurt though! The Garmin equipment was pulled out of the aircraft when it was parked and they've been properly stored since. They were relativity new at that time too.
It's likely that very few parts remain of the original engine besides the data plate, especially true if it ever got a factory overhaul.
A Garmin 430W (not to be confused with the non-WAAS version) still fetches a premium on the used market, at more than $7,000 on eBay. Add the rest of the avionics in and you could get at least $11,000 slinging them on eBay.
The engine core is worth at least $5,000 if completely runout. Engine accessories can be sold off separately. Figure you can sling the prop for another $1,000 and the airframe for $4,000.
My rule of thumb is that if the price of the whole is less than the sum of the parts, you can't get too burned and should pull the trigger.
Yeah that's pretty much how the seller arrived at that number. Not a bargain, but not far off base either...