The last sled I did this on was a 91 Indy 500. But there are only 2 mounting points 3 inches at the rear and 1.5 inches at the front.
So if I drop 2.25 inches how much forward should I go. 1/8th on a inch or will it work if I just go straight down.
I remember this feature on the older indy's, but I can't remember how much offset the holes were as they dropped. A couple of other things to remember if you are lengthening the track. Your original set-up has a progressive downward angle already, when you lengthen it the rear contact point of the track will be considerable lower. Depends on how much "lift" you are looking for? IMO, the most important thing will be getting the position of your front mount in order to maintain the correct "contact patch" on the base of your track. Another factor will be if you plan to raise the front suspension or leave stock. If you make your own brackets leave yourself room for multiple holes for trial. I put an M-10 skid in my SX a couple years ago, works and looks great, take your time.