I have 5 deg Pro One raked trees. The previous owner installed the trees and 2" over tubes, which turned out to be just about right for the trike conversion and my taste. Some like to go to 7 deg to make steering even lighter, but some also complain that 7 deg makes it a little too squirrelly. In general more rake in the trees will reduce trail and make steering easier. A trike conversion without raked trees can be just too 'heavy' for some. Frankenstein recommends 7 deg trees and have them available. One thing I really like about the Frankenstein is that it is very basic and you can make your trike into whatever you want - from a chopper to a cruiser with a body and storage. You can start out simple and add later as funds permit if you want. The Sportster makes a really nice trike.
Trikes are a blast to ride, and I think in many ways safer than 2 wheelers. I've had many trikes since I was 17 - from VWs to V8s, and quite a few two wheelers in between. Now that I'm getting up in years I'll probably stay on 3. You don't see a whole lot of Frankentseins out there, so you will get a lot of comments and questions - be ready! If you've never driven a trike, try to take a course and take it real easy until you get used to it. Very different from a 2 wheeler - you steer, not lean.