Yes I think the old A and B series production line were years out of date. The K though was all new, to tight tollerances. I had a sideline in buying rover 200s, head off, skim and rebuild (as long as the engine hadn't overheated to soft). Mostly I found the radiator was knackered - nothing to do with the engine. Also I repaired dozens of gearboxes - a Peugeot box adapted to the K, first motion shaft bearing, easy fix, I used to have them on rotation. The 8V K was snails pace, if you had the 16V k series it was anything but slow.I've had a couple of BL cars (and am still using a Marina), nothing exiting but they do what they need to do, they were often rough and agricultural when compared to the foreign cars of their time.
My previous car was a 1275 Hunter with overdrive, on paper it's similar to the Marina but it was a whole lot nicer to drive, more refined, more power, more relaxed due to OD, and many parts (suspension, wheels, brakes) are interchangeable with Ford making it easy to find used part for cheap motoring.
K-series is a great engine but needs some sympathy which is often missing from motoring public. It's also easy to go wrong when rebuilding which is why many garage won't do engine work. I had a 214 Sei, when I got it the thing was dog slow, a 300 mile motorway run blew the cobwebs out then it was fun and nippy but a bit low on power, sweet but nothing special.
A lass was living with me last year, she had picked up a Rover k-series 214/216 for daily transport. I got a panic call to say a water hose had blown off. I went out, refitted it and told her to get it to a workshop asap to get it checked properly. She didn't I got another call 3 months later to say it had popped again, this time it blew the headgaskjet. We took it to the local workshop - they had fittted a replacement motor for the previous owner so he could sell the car - they had so many problems with it when he owned it, they refused to even look at it. The car got scrapped because of the headgasket. For comparison I bought an old VW golf with a blown headgasket, I did the work in an afternoon on the driveway and didn't even need to check the head for damage as I knew it would be ok.
A lot of British industry in the 60s/70s (cars and bikes) could be easily recognised as a modern version of the pre-war machines. The overseas industry had been wrecked by WW2 so their factories and cars designs were built "new" by the 1960s - which is why Japanese & German cars were years ahead of the UK in development.
A magazine article I saw reported that machines from a motorcycle factory had been bought up and the new owners were wrecking crankcases when they tried to use the machines to drill them.
After speaking to operators at the old site, they found the vertical drill needed an old floorboard held against the motor when in use to stop the drill shaft vibrating - the machines were so worn out they were otherwise unusable !
I rebuilt an 8 valve that had broken its cambelt, get towed home in gear. The conrod was in hundreds of bits. Second hand head, rod and liner, clean and rebuild, went for years.
I had a 1.6 K mini in here once, on Dellortos. bits everywhere. It turned out the Delortos had sucked in the clasp from the makeshift air filter - that got a used piston and rod, don't remember if the head survived. It took me 3 24mile test drives to clear the oil, antifreeze, water from the exhaust, but boy did it shift - it was eating gears as fast as I could change them - a right hooligan machine...