Mark VII's and Mark XIX's both have adjustable triggers in them.  For either, you can get longer barrels (10").  Like fuatos said, for the Mark XIX, you can get the other calibers as well as conversions (or you can buy the whole damn set, but with something like 6 barrels, I imagine it is damned expensive).  The Mark XIX does have a scope rail as part of the barrel, complete with the crosscuts for weaver style mounts.  Also, since the Mark XIX is based on the Mark VII, parts for the Mark VII will work in the Mark XIX.

I have shot the Mark XIX .50AE, and it is a fine gun.  I just didn't see the need, so I bought a Mark VII .44Mag.  Love to shoot the gun and you always get some looks when you pony up to the line and let the thunder loose!

Either way you go, you will be getting a hell of a weapon and will enjoy it a bunch.

[url]www.magnumresearch.com/[/url]

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WWoodworth

T-Man,  The Mark VII has what could be considered a rail on top, but it is not as wide as the weaver mount.  More like what is on top of a Marlin .22 I have from about 16 years ago.  The Mark XIX is full width!  You should be able to get a Mark VII for somewhere around $850 or so new (I think).  As far as trading goes, worth is in the eye of the beholder.  One doesn't always have the luxury of comparing book values.  It depends on what each individual involved wants.  If you will be happy with the DE, by all means get it.  If you think you will regret the trade, purchase it outright.  FWIW, I traded a used .45 and a used .38 revolver for mine.  I had less in both combined that the price on the new gun, but value of the trade may have been a couple of bucks in his favor.  But since I never used the .38 and didn't care for that .45, the deal was perfect for me.  Just my $.02 worth.....

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WWoodworth