Ok, I'll throw u a bone. I picked up this plane cheap, got the Magnum 91 on sale too. I am going to fly it stock for a while to see if I really want to make mods (currently a yes after 10 flights).

Here is the only thing you will find on retracts in the F=22: http://www.rcuniverse.com/forum/m_52...8/key_/tm.htm#
This guy did a really good job, but not enough information.

These threads show retract installations and engine discussion in similar sized propjets, you may be able to pick up some ideas from them:
http://www.rcuniverse.com/forum/m_6938168/tm.htm
http://www.rcuniverse.com/forum/m_2186098/tm.htm start looking around p.49 for the retract installation
http://www.rcuniverse.com/forum/m_8095663/tm.htm probably has the best description (and pics) of retract installation.

Also, this has more to do with setup, but its an important mod:http://www.rcuniverse.com/forum/m_52...22/key_/tm.htm
It talks about shimming up the motor mount (good idea), and some people talk about using the 91fx with a Jett muffler. It is the biggest thread about this plane.

Now, go read until your eyeballs pop