This is a hit and miss thing. Suspension systems are designed with exact angles and distances in mind. When you change both the length of travel and angle of the shock you have a lot of things that you have to check. One of the biggest issues with the longer shocks on stock a-arms is that even if you modify the mounts so the shock fits, the shock may have too much travel to work safely. The bump stops in a properly working system will stop suspension travel on bottom-outs before the ball joints and all that get pushed to angles they can't handle. The longer shocks will have more travel than stock, and might not hit the bump stops soon enough, causing stuff to bind up and break.
There are a bunch of other factors that are difficult to measure until you have everything in hand, set up, and all that. So you are taking the risk of spending this money on shocks, and adding those mounts on the a-arms, just to find that there isn't a way to make them work safely. The most important thing when you're doing custom work like this is to make sure nothing binds up at any point in the full range of suspension travel. Spending the money on the shocks and finding out you can't use them sucks, but a $10,000 medical bill and being off work for several months because a ball joint let loose at high speed and launched you over the handlebars head first is a hell of a lot worse in comparison.
