I never took measurements of the museum xylophone and built this on memory and guesstimation, so please feel free to do so on yours as well.
Step 1: Measuring, cutting and sanding
I cut the 2x4x8' as follows
-- 36", 34" and 26"
--30", 24", 22" and 20"
--28" and 32"
the first 2 equal 96" exact, so when cutting split the line to get it close... you could break them up differently to get better measurements, but come on.
Step 2: Assembly
Find the middle of the rope and leave about 1' of slack to tie the xylophone off. Start stapling the rope at the marks on the first "note" and leave 1 1/2" of space between notes as you staple. (why 1 1/2"? because that's what the scrap wood is). Making certain the centers are kept in line. Don't cut the ends at the long side, as they will be used for tying up the xylophone too.
Step 3: Tie it up and play
When you hang it, the angle and "droopiness" of the xylophone will have an impact on sound so play around with it to get the best sound from yours. I sanded down the dowels and used them as mallets, but you can use whatever is handy. Have fun, my daughter loves hers.