Though the mods Dan lists are likely giving him more satisfaction than were the gun to be stock, it seems some of those mods were made for, and are more useful for Field Target shooting. There is nothing stopping you from buying a Marauder and using it in its stock configuration for 25M benchrest. NONE of the mods Dan listed are required, or even really more useful for benchrest shooting with that model, assuming you luck out a little, and get a barrel you like. And, IF your barrel is not good enough, you can even exchange it with Crosman for another.
I have a bone-stock .177 Marauder that shoots well with adjustments I made to the striker stroke and spring preload, transfer port throttle screw, and the various trigger stops and tension settings. The gun is not quite as accurate as my dedicated match guns, but really not so far off. Though it likely won't shoot many 250's indoors with it, I'm sure it can hold its own in many competitions outdoors in breezy conditions, where wind doping skill counts more than intrinsic pinpoint accuracy anyhow.
IF this particular gun's accuracy needs further improvement, the only requirement is a better barrel, there are NO other single improvement that would even approach the result of a great barrel for this gun, and then, I'm not sure how much it could benefit, since its darned accurate in stock form.