Last year for the 401 in the Wagoneer was 1978, almost impossible to find one now though...
If I'm not mistaken, I think the 401 was physically the same (dimension wise, etc) to the 360. If so, the 401 would be a relatively straight forward swap into the GW. Are you sure the engine in your GW was not a replacement engine?
My personal GW is a 1984 with 85,000+ original miles that I paid $500 for. It is a gem and a 'keeper'. I'll never be without one again, despite the less than ideal fuel mileage and needing a few parts replaced now and then. I figure that all the money I saved on a new vehicle of questionable reliability and safety can be wisely invested in a legend that I feel safe in.
Seems like the common thread among these GW reviews is that although their vehicles break down a lot, they love them nonetheless.
As for me, every time I get the urge to buy a GW I just look for one out on the road. Invariably, it will be driven by some old guy. Wearing a hat. Seeing that usually cures the desire to go out and buy one, at least for a while...
Anybody living in Colorado in 2003 remembers that week long blizzard storm. I think it was dubbed the "St. Patrick's day blizzard". We have a 1986 old Jeep Wagoneer and a 1997 Jeep Cherokee. Both have 4 wheel drive. Guess which one actually drove through 3 feet of snow? Yep, the "old man". The newish Jeep couldn't get out of the driveway. The old Jeep tore up the unplowed street and got my dad to work that day. He was the only one that showed up, and he had to run the place without anyone else. He's taken that old Jeep deer hunting, 4 wheel driving, snow plowing and mountain climbing for over 20 years. To this day, it's still the best truck we've ever had.
I owned a beautiful 1986 Grand Wagoneer for many years. I loved that car, and I spent a lot of money just maintaining it.
There are some issues... like the water leaks in through the front cowl drains that get plugged; the constantly breaking window lift tracks (plastic) and the most serious I came across was several that had ended up in junk yards from electrical fires.
I did a lot of research on this and after talking to a lot of people here is what we concluded: the fuel line passes close to the exhaust lines in several locations. Originally the fuel line is held away from heated lines by ties. However, sometimes when work is done on the vehicle the ties are cut to access areas and the fuel line is not properly re-secured away from the hot exhaust lines. If you own one of these this is worth paying attention to.
I still think they are one of the most attractive classics!