Bean ,
Our first batch of 8 , part of a cancelled California order ; came with long nose gear . Looked like they were 'waddling' around the taxiways . Flew ok , but we were told the long gear was so that 'Parrots could use airbridges . Which we did , mostly in Germany on the short IGS [Internal German Services , out of Berlin ] routes . Proper Highlands and Islands we used the airstairs , which worked well . By the time the second batch came , to finally retire the 'Budgie [748] ; someone at Woodford had actually looked at an airbridge ! Of course the short gear was perfectly suitable , and saved weight . At last we did not 'waddle around anymore .
Think they were also interchangable . Seem to remember one or two of the first batch came out of overhaul with a short nose gear .
Good machine , but built West of the Pennines with 50p gadgets instead of £1 gadgets , thus the sobriquet Advanced Technical Problem .
'Fraid I'm not an engineer and also cannot answer your second ques.
rgds condor .