A chain is 100' long in the USA.
A bushel is 8 dry gallons in the UK and 64 pints in the USA, but a USA pint is not equivalent to a UK pint, so they translate differently. A US pint also has 20 fluid ounces, and a UK one has 16.
A Swedish inch was bigger than a British inch, and the "foot" varied all over Germany.
That's the whole problem with how you have defined a mile in "pre-grouping days": there were national differences and cultural biases underpinning the system, with chaos potentially ensuing - hence the creation of a unified system based upon (originally) the distance from the north pole to the equator, following a circular path based on the surface of the earth. It was 1/10,000,000 of this. It has been revised since, most recently in 1983 with reference to the speed of light in vacuum and the distance travelled in a second.
The inch was defined to be 25.4mm as a way around this, but a mile was whatever a national government defined it to be until more recent times. It started with the Romans, but their mile was different to ours, being 1,000 yards (mille passus, or 1,000 paces) or 5,000 Roman feet. And a nautical mile is longer still...
The definition of a "statute mile" as 8 furlongs is a late Tudor creation, and it was the surveyor's rod, not the chain, which was the key determinant of a furlong. A rod is, of course, 1/4 of a chain, and is 5.5 yards. Originally it was 5 yards, but the yards (and feet, and inches) were longer until 1593 when Queen Bess redefined them. The chain had been 20 yards, being a multiple of 5 yards, but when what was previously 15' long became 16'6" long under the new definition of a foot, the rod and furlong (and mile) maintained the same absolute distance, but were redefined in terms of their number of subsidiary units. (In case anyone is wondering, the "rod", also know as a "pole" and a "perch" is generally considered the be the longest length of pike that a footsoldier can use without difficulty. Since the aim of a pike is to put as much distance between the enemy stuck on the pointy bit and the pike-wielder, that is the usual length of a pike!) That this system was still in use in this country 300 years later is testament to the inertial power of any written standard.
The base 10 nature of metrification is, yes, an extension of five digits on each hand, which was the basis for the Roman counting system (V is the shape between forefinger and thumb on an extended hand, X is one V on top of another which has been inverted) although as the Roman counting system didn't include the concept of zero as a place marker, that doesn't help much. Base 12 would have been so much easier, but our counting system is indo-arabic in origin, and they were counting on fingers.
It was the lack of any agreed consistency amongst nations over weights and measures that made something like metrification inevitable. Base ten was also inevitable given the number of digits on each (normally replete) hand. The mile was internationally agreed to be 1,609.433m in 1959. This wasn't done to "suit the metricated", just to actually define the blessed thing consistently.
As I said, I use whatever is convenient, but as I consider myself to be reasonably scientifically literate, and therefore happy with the SI units. Because of my interest in railways, I have had to learn a lot about "imperial" units, and view that as one of the many benefits of the hobby, without the need to prejudice myself against either system.
Learning about other systems, and cultures, etc, only improves insight into the human condition: variety is the spice of life!