Mellotronists

so I'm cleaning up 1407 - pretty much disassembling everything that will 
come apart and doing whatever's necessary to get it nice and shiny 
(mostly polishing aluminum).  I've gotten down to the tray that the 
headblock rides left and right on and discover that the tray appears to 
fixed to the frame with pop rivets. I'm a bit surprised as so far, 
everything else has been screwe/bolted into place.  I guess for some 
reason, this is not meant to separate from the frame, so I'm going to 
have to remove the spill box to get at the screws on the rear "comb" 
tape path assembly.  Does anyone know why this would be riveted and not 
screwed into the frame?

thanks,
john

PS - it's become obvious to me that I'm going to have to remove the tape 
set from the tape frame to properly clean it up.  Is there a good method 
for that or should I just pull the tapes out,  toss them into the corner 
and try to sort them all out later?