I'm including some pics of my bike, a 1976 TL-250 with an XL-350 engine. I adapted the 350 header pipe to work with the super-quiet TL muffler. The stock TL airbox was used by doing some carving on the carb boot. The head fins were trimmed to fit the TL petcock and the trials tank was shaved to clear the 350 points cover.
It's an easy conversion and a fun bike. It will climb anything you can throw it at and is great for tight trail riding. After riding it initially, I found it worked much better with a 250 flywheel and also the 250 cam which has less duration and really makes the 350 a tractor. It still revs very high if needed which is seldom. It's hiway registered so I can cruise to the hills nearby. Stock TL sprockets allow a 35mph cruise and top speed about 50. You may use any or all pics. Let me know about the seals. Thanks, Chris Robertson