I had a 1997 4.6 plus 8 long door for ten years, when I got it at seven years old it had done less than 7000 miles, I ran it for a year, never had an overheating problem. Then had it chipped and never had any problems, it ran as sweet as a nut and was the best plus 8 I ever owned. I'd had a 3.5 and a non cat 3.9. I sold it last year with 28000 miles on the clock as it was very thirsty and having retired didn't think the constant visits to the petrol station could be justified. It also was starting to need some cosmetic work, body, new s/s wires etc.
I have regretted selling the car every day since, I miss the oomph, the burble, just everything about it, bar the fuel consumption, was awesome. Some others on this forum may testify to the acceleration/ speed of the thing.
I now own a 2007 plus four which is lovely and I get over 45 mpg but it isn't an 8 and never will be, if I could afford a 4.6 plus 8 I'd buy another one in a heartbeat, IMHO they were the best plus 8 ever built. Go for it, you'll never regret it.