Just a quick update on this.
After deliberating for a while, decided to get the job done professionally and glad I did.
Had the work done at P & L Motors in Warminster (Wiltshire). Recommended to me by someone who buys and sells Chrysler 300s. Even though they are just over an hour away from me, well worth the trip.
Excellent service by P & L, they used a clever telescopic ratchet socket on a swivel joint which made getting to the rear nuts in the engine bay relatively simple, without the need to remove anything else. The ball joints were split with 7 or 8 very heavy hits with a hammer (much harder than I would have expected). Loosening of the shock absorber struts was also absolutely necessary in order to remove the 2 bolts.
P & L Motors have good knowledge of working on Chrysler 300s so would definitely recommend, even if you have a distance to travel, like me!