We still have all the AGD dimensions for pumpmag milling - Renie machined my rail for meNice one GeeTee, milling the rail is probably out of the realms of DIY for most of us mere mortals though.
If you can find an ASA adaptor plug for the Spyder front block it could be drilled and threaded to accept a pump mounting rod.I'm cutting half the top tube off mine and have tapped the rear of the bolt so I can attach two brass pump arms to the rear. PVC over the barrel like a phantom. If this works and feels 75% there I'll jb weld some guide rods to the body where the upper and lower tubes meet and put some springs over the top which will ride in the wooden pump handle which will either cover or replace the pvc.
If not I'll be hunting for a trilogy undercocking kit but they are getting scarce.