For the ASA, getting an On/Off may not be stock, but it is extremely convenient if you go to sweet spot the reg. Leave the back block as the stock one, that's one of the defining characteristics of the old cockers (you can almost tell the year by the shape of the back block). I would suggest upgrading the trigger frame though. The one I had on my 98 cocker broke at the ASA screws. The plastic just cannot take the force sometimes, especially with larger tanks (I had a 48/3000 HPA tank on it at the time).
If you're worried about the steel braiding, why not use a macroline? You can match the colour, reduce a bit of weight and still maintain a good look.
p.s. Keen, where did you get that trigger frame?
Think of it not as "hopelessly outnumbered", but rather as a "target rich environment".