Nice work so far  

 As for the bulb length.. its a very odd size.   Your best plan is to replace the lamp
assembly with a modern width unit.  That is what I did.  The bulbs I found were all 
for 24",  and would not quite fit into the smaller factory assembly.
 Sadly, the lamp assembly I choose doesnt seem to want to fire the bulb up all the time.   Make sure to get a good quality lamp assembly.
 I tried the  f20t12-bl   White Blacklight bulb,  and thought it was way too bright.
I then changed it to use a full sized Black Backlight bulb tube... and even that seemed
a little bright.. but much much better.   
 (Im going from Memory of the original machine from when I was 6 or 7 yrs old... as well as my personal artistic viewpoint/opinion of what I remember and or should look like)
 I suppose if you were on-location,  with lots of ambient lighting/sun,  you would
might need the extra light of a  WBL bulb.   This may have prompted a change from
the original design, to a new spec due to complaints.
  I prefer the dark night look.  IMOP The sky should look blackened, not yellow/green (which happens when lit up with White BL bulb).  The blue/green backdrop
art should blend in well,  without standing out too much.  Much like viewing things
at night would be.
 I believe there may have been a few revisions to the machines..  because Ive
seen machines which had blue light blubs in a screw-in socket assemblies. 
 So, chalk this up to personal opinion...   but I wanted to warn you..   because I 
feel Ive wasted $20+ dollars on a bulb that I will never use for this game.