Markers from the earlier eras (year 2000 and thereabouts) featured more wide-open designs that were very easy to attach on other markers. Frames were a popular example and I performed a number of mods such as those over the years. Unfortunately I don't have pictures of most of them, but I do have some of my more recent ones here on this page.
Here's one of the completed Angel frame mods for the Shocker. The frame here was from an old 2000 LCD I believe, mounted to the gun using 1/4"-20 screws.
Here's a gun with a complex setup of gaslines, connecting the HSW foregrip to a horizontal Max-Flo reg, with an NDZ drop-kick bottomline. I also added a custom LED and powerswitch on the back (not picutred).