Motorcycle Repair: 73 Sportster Iron Head Rebuild Project, xlh sportster, transmission area

Question
I have a 73 XLH Sportster rigid frame that I purchased in 1980 in a basket.  I would like to build the engine so the bike is fast and reliable.  When I laid out all the parts I noticed that the cases have been welded in the rear transmission area.  What I need to know is what is the best route to ensure that the cases don't leak and how much can I hop up the engine so that it does not wreck the cases again when I push it more than normal. Any information is appreciated

Answer
Your cases were probably damaged from the trans locking up, not a motor problem. Many iron heads from that period were hopped up and stroked for more power, without problems. I have build many of them and were reliable. How much power are you looking for for your motor?
I would start by having the cases checked to make sure the weld is good so it doesnt crack or break again. You can fit the cases together, without parts and see if they fit tight together and there are no gaps.If you have gaps, then they were warped when welded and would have to be replaced.
Mike