lining up two skids side by side is not the best way to go about things. shock condition, spring condition, and settings all factor in and you most likely wont be happy attempting this method. you want the actual dimensions out of the donor sled, period, along with more advise.
those swiss cheese drops your referring to arent available that i am aware of. those holes in them for the life of me i cant see any use for. i think they were a standard bracket drilled to meet other manufacturers dimension. i have an extra set around but doubt they would fit a stock tunnel. i make my own drops from aluminum plate. unlike some, i do add a provisional hole or more just in case but those holes are incremental and keep withing the arc of the suspension, not just random.
i was actually curious as to what track you had selected. you do realize that the 153 track is a 3" pitch and there is just about no way your going to get 3" pitch drivers in the stock tunnel without a drop and roll or extended chaincase. hence the hint in my first post about decisions. you need to stick with a 2.52 pitch track no more than 2" unless you modify elsewhere. 156 or 159 are good choices but rail extensions are limited for the 156, you need to move the 153 skid back a bit more. you can also trim a 155 track and swap drivers to 2.86 pitch if you allow for the setbacks when installing the 153 skid.
as mentioned, lots to think about.
