Got a set of long tails that i am going to cut down for this KE exhaust install i am working on. I wanted these things to be LOUD. So i decided to keep the tails as long as i can. They didnt line up perfectly with the original thru hulls so i plan on mitre cutting to get them in line. I will be welding back both inner and outer pipes. Is there anything wrong with only using a short piece of rubber exhaust to make the connection?

I don't see why that would be an issue! Just make sue the two metal pieces don't touch, otherwise they will vibrate and make noise you don't what to hear!

If your doing all that cutting and welding I would just run them thru the transom and use no rubber. You would have dry pipes to the tip and be "loud".