Flatslides are great 'Trap. They were actually on my Cooley and will go back on once I get my smoothbores back from Bruce. I had sent him a set I had purchased off a board member but they ended up being buggered (basically to the point of being unuseable) so I picked up another set and they are on their way to him hopefully. Those flats were actually NIB purchased from a local guy I know. Never have cracked them open so I am unsure of jetting. I know they are perfect for the 1085 motor in the cooley.
Speaking of, what's your progress on your motor? Did you ever find the D port head?
I won a GS1100 D port head on Ebay but the seller dodgedude_97 has not contacted me since I won it back on May 25th. It was worth a shot, the seller has terrible feedback rating. I will get my money back eventually; the D port would have been better. Once I get that squared away I will need a set of Flatslides