Shred Man,
I own a Twist 3D as well. I changed the engine from an O.S 46FX to a O.S 61FX. I followed the instructions from the beginning, and had no issues building the plane whatsoever. I do not see a reason why you should take extra/different prrecautions building the Twist, for as far as mounting the Saito goes.
The Twist is a very capable plane. Not specifically build for 3D, but depending on your qualities/skills, it will let you do some wild things with it
Don't underestimate this "wild yellow bird".
Do you know there is a Twist 3D forum??Check it out...there are many, many usefull postings there as well..and the group active there, is always ready to help you out with questions regarding the Twist, including yours truly
PM me if you have any more/specific questions whenever you want.
Enjoy this wonderful plane...you are going to have some serious fun!!