[Collins] Collins S line help?

[Lee]

Howdy Folks
Having just got my Call VK5ZNA I am looking at getting  some S line gear.  I 
have had a look at the circuits for the
75S1 , 75S3 and 75S3B/C and a part from the Q multiplier and the use of  the 
6EA8 instead of the 6U8, I don't see
a lot of difference between these. Now as regards the 32S1 etc I don't know 
very much. Please tell me what is the difference
between various models is when it comes to operating. I read you can 
subsitute the 6EA8 for the 6U8 in the 75S1, does it make any difference?

I am getting a 75S1 but don't have a 32S1 or 2 or 3 which one do you folks 
suggest? and will it matter? I have been tinkering with radios since I was 
in High school
 with the last 10 years spent on computers and am looking forward the 
renewing my interest now that I have a Call sign.
BTW does anyone have any spare xtals for the 75S1?
73's  Lee.