As Far as I know, Sea World do still run their Shuttle Down to BGT, However I am not complety sure if its Free though, you might have to check that, and I am sure you can get the times of the shuttle at Sea World too
I have been to BGT now about 8 times(Quite an achievment for someone who lives in England) And I would'nt worry about Crowds. From past Trips, I have never experienced any large crowds before, I went in August lasy year expecting Crowds to be Crazy but got the opposite, they were quite handable actually, Montu was about 5-10 mins max,Kumba was nearly Walk On,Gwazi had 25 mins queues for Lion, but 5 mins for Tiger???Scorpian was walk on and Phython was about 10 mins too, The 3 Water Rides also had short waits, suprising too as it was a boiling hot day.
Well, have Fun on Kumba and Montu, they are excellent B&M Coasters.