I put 12.5" shocks from a suzuki intruder 800, on my savage, and I like them a lot. Softer ride and I like the looks, but here are 3 things to watch for. I imagine these apply to progressive shock upgrade too.
First, you have to grind a little metal off the front of the belt guard, top and bottom both to avoid rubbing. I also replaced one hex -head engine bolt with a round-head allen bolt at the bottom curve of the front belt pulley.
Second, the oil level site glass reads low because of the tilt of the engine. Check oil with front wheel on a 3" rise or brick. (Pain in the ...)
Third, I used to get 100 miles before hitting reserve, now I hit it at 85 miles (1.75 gal US). (ran out twice before figuring that one out).
I may try shortening the on position petc0ck tap to remidy this, as I like 100 mile to reserve.
Anyway, just wanted to point these things out.
I still think it's a worthwhile mod, I like it better anyway.