Since the XL is designed for a gas ram, how are you going to keep the ram ends centered on their bearing surfaces ? Spring guns don't have the "sockets" to keep the ram ends centered.
Even if you can get the parts from Crosman, will the non-Crosman ram your ordering fit the XL parts ?
The XL's piston has an internal socket bored to fit the end of the ram shaft. And the rear plug of the XL's reciever is bored to except the end of the ram body. Then there is a thin washer that goes between the plug and the end cap (Crosman calls that cap the "tube cover" in the Super Streak parts).
If one is wanting to save the original Super Streak parts and just do a parts swap, while not modifing existing, or machining new parts,.. not only is a ram of the same dimentions as the XL needed, but I suspect an XL piston, rear plug, and washer will be needed too. And, we just found out they made both plastic and steel "tube covers" for the XL, what else is differant about them ? Is the Super Streak's "tube cover" the same installed length as the XL's

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You sure like a challange don't ya !
Paul.