xkwox,
The kit that Hough bought and used was the frame mount kit. The engine mounts to an adjustable mounting plate that bolts into the main v section of most bicycle frames. GRUBEE does make a rackmount I believe it can be purchased from
http://www.bicycle-engines.com You need to be aware that if what you are looking for is a rack mount, that the Honda GXH50 will be mounted to it with the exhaust hitting you in the back when you sit on the bike. You will probably need to make a custom exaust system to remedy this. There are several threads here that show how members have done this with various motors. Do some searches to find these solutions.
I may be wrong about being able to purchase the rack from bicycle-engines.com I would have sworn that they were offering this option but it no longer seems to be listed for purchase. Maybe they sold out. You might want to give them a call to find out the status of this rack. In the past bicycle-engines.com have not been good with responding to e-mails so a call to them would be the way to get the information about the rack. The person there with the answers is Josh.
As to the two items from Stanton Inc. You don't need either of them if you purchase the 4-stroke mounting kit from bicycle-engines.com
good luck with your project,
scully