Welcome to the forum.
Here's a link that might provide you with some basic installation instructions. http://motorbicycling.com/showthread.php?t=13504
They've all been posted here numerous times. You can usually find answers to all your questions by using the Google Custom Search at the top of each page. Just type in a keyword/s and you'll have plenty to read on the subject. We're always here if you are unable to locate the information you need.
Here's another link to an old thread that contains some very good engine mounting ideas where oversized or curved down tubes are concerned. http://motorbicycling.com/showthread.php?t=6427