The 3-way valve isn't a hard thing to do, as long as you've delt with PVC in the past. There are pros and cons to both of these cleaners in your situation. I'm a Polaris dealer so I'm very familar with the products.

360: Proven - You will want the sand/silt bag for sure.
340: It's been out for several years, but the 360 is more durrable and easier to work on. Suctions cleaners are sometimes better for fine dirt such as sand and mud.

If you have a dedicated pressure line, have you considered using a Polaris 280 with a booster pump. I think this would give you the best performance.

Josh