We did have the arch added to our 258 and we used it for wakeboarding. You are right that its really not a ski boat but it made a great wake and our kids loved it. Our arch was built with the boat and from what I was told, they reinforced the body at the factory to help with the stress.
If you have the solid arch, I would be concerned how structurally sound that would be for towing. We needed to fold our bimini under the arch to ensure the tow rope did not catch. I think you would need to rig it going forward rather than back. We used bungee cords to hold the bimini.

The wake was a little rough but at about 22 mph, my son could jump from edge to edge. If I can only convince him to try it with our 338!

Just my 2 cents.
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Jnizi
2007 Vista 338 "Better Yet"
Previously:
2007 Vista 258 " Just Right"
2005 Horizon 230