Besides Alex B's short video embedded in his report/blog (
https://ctccambridge.org.uk/blog/2016/05/14-may-bryan-chapman-memorial-600km see his post above) which shows one of the sharp climbs NW of Llanidloes, Adam Watkins made one that year too which will give you a very good 'feel' for the ride, albeit he is up the front end (think <100 hour LEL completion types) - link:
https://www.youtube.com/watch?v=vyotlUgS8FM Inter alia gives you an insight to the fantastic hills over to Machynlleth, the turning and intial steep bit up to Kings, the set up in the YH, Barmouth bridge, "Ticket! ticket!", [Edit - thank you, @Jasmine] Telford's suspension bridge across the Menai Strait, and much more (including overnight cold). I notice he stopped outside video features) @Flatus 's Spar at Carno (closed at 3am!), before Aberhafesp.
The video of the Rapha riders' Bryan Chapman 'tribute' ride (NB in March) is here:
https://www.youtube.com/watch?v=R8GoL8UzIj0 for more situational awareness.
Alex B refers to wilkyboy's 2013 ride report
http://www.16inchwheels.uk/2013/05/18/bcm-2013/ which is (he says) a rewrite of his post on yacf
http://www.16inchwheels.uk/2013/05/18/bcm-2013/ in a thread which stretched to 38 pages: required reading (NB '600' route has changed).
It was my first ever 600 back in 1993. I still think of it as a good beginners' ride.
And you rode it again 24 years later. A good middle-agers ride too then.