Alex,
Those are good suggestions and definitely things to be considered. Thanks!
Popsrr,
I just glued (Carpenter's Glue) the spacers to the 5/8" plywood top, and the QuietBrace to the spacers - at the same time. There was no need to add additional weight to keep everything in place and make the excess glue ooze out; the track and QB weight were sufficient. To add the glue, I just lifted the QB and track slightly, slid the spacers out, added the glue, and slid them back in place - one at a time.
However, I did not glue anything until AFTER I had the trestle bridge finished in case I had to make any adjustments to the track. But no adjustments were necessary. In the meantime, before gluing, the spacers just cooperated nicely and stayed in place 
.
That sure brings back memories . . .
March 26, 2011 - Spacers for one of the two grades.
April 16, 2011 - Track at trestle site on temporary supports.
July 17, 2011 - The trestle and grade at Etieca Valley complete (at top of picture), and the grade at Villa de Rocas ready to have its spacers glued.
Alex
