It's a commonplace in manufacturing that unless the design-engineers work VERY closely with the manufacturing and production management/engineers, there WILL be problems with the product.
That may be the case with the FoMoCo 500.
Having said that, I've driven Chrysler, GM, and FoMoCo products WAY past 150K miles and 10 years--then the wear-parts start, ah, wearing.
Currently have 2 FoMoCo's--one 15 years old, one 5. Both over 85K on the clock. Replace only small wear-parts.
No other problems.
I drove a Thunderbird back in the mid-eighties and into the nineties. It had 250K miles on it when the speedometer gave out.
I might still be driving it, but a young mother leaning over her seat to scold kids whacked me and totaled the car out. ;o)