Generally, when reducing the length and going from an armlock applicable grip, the biggest issue is how it changes the overall feel of the putter. I have not measured the component weights of that putter, so I can’t be precise in what the affect might be by doing what you’re doing. I will assume the head is pretty heavy to offset the extended length and heavier grip. When you shorten, you may need to play around with different grip weights to get the balance and feel you want. There are counter balance options that can help dial it in (Super Stroke Traxion type grips with the weight adjustment options). There are also lead counter weights or the Tour Lock Pro products that can help. Again, I am assuming the head weight is heavier than normal. If the head weight is more normal, like 350 grams or less, then most likely you will not need to counterbalance.
6 degrees of loft is a lot, but if you forward press, or can get the proper roll with the loft the way it is, then no worries. Our research has shown, again generally speaking, that 3 to 4 degrees of loft is optimal for the truest roll. Of course, every individual is different and you need to assess your own stroke to know what loft is right for you.