I was going to recommend a yard to you that's about an hour from me, and they had an '88 780 with a B280F engine with only 90,000 miles on it, -but I just called them and they crushed it a month ago.

However, I did find a few other B280 engines in the area using a salvage yard search at www.car-part.com. It would be worth your time to run a search here and see what's available in your area. Distances and prices are marked, as well as phone numbers of the yards holding the parts. I just did a quick search and there's a few B280 engines in my area for about $550 each.

Also, if I were in your shoes, I might consider going with a B230FT conversion. I personally have a B280 in my 780, a B230FT in a 780 (accident vehicle I'm hoping to restore), and a B230 in my 240 wagon. I have to say that the B230 is the easiest to work on. The B230FT is a bit harder than the B230, due to the turbocharger and extra hoses, but hopefully you aren't taking your turbo off the car on a regular basis.

If you're looking for a nice ride and great gas mileage and very little maintenance needs, I'd swap in a B230. If you want the sporty feel and quick acceleration, I'd go with a B230FT or replace the B280. The conversion shouldn't be that difficult, so long as the donor car for your B230/B230FT is an '88 or later vehicle, as it will have the later style wiring harness connectors. Also, the driveshaft is different between the V-6 and the 4-cylinder engines, and it's also different between the Fixed-Axle and the Independent Rear Suspension (IRS), so you may find a great donor car for your engine and tranny swap, but may need to find a driveshaft from another vehicle to match correctly. I can explain further if you need me to.

FYI, I would consider a B280 to be "high mileage" at 300,000 miles, and I would consider a B230 to be "high mileage" at 500,000 miles and are capable of millions of miles if cared for (I.E. Irv Gordon). The Turbos require closer scrutiny as I've seen some that have been badly treated by 150,000 and a few that were still quite healthy at 200,000. However, if you're considering installing a B230FT, change you head gasket and have the head machined flat before installing it (unless it was done in the last 70,000 miles). In my personal opinion, the turbocharger doubles the wear-&-tear on the engine.

Just my two cents.
God bless,
Fitz Fitzgerald.
--
'87 Blue 240 Wagon, B230F, 278k miles.
'88 Black 780, B280F, 149k miles (off the road for a stuck brake caliper).
'89 Black 780, B230FT, 94k miles (accident vehicle I'm hoping to restore).