Congratulations!
Q. What are you missing with the mod to remove the rear doors?
A. The single engine climb rate.
The Skymaster two engine climb rate is great. In contrast, the single engine climb rate is poor; about 150ft/min. If you unexpectedly lose an engine on takeoff, and you lift the gear to "clean-up" the airplane too low to the ground, the drag from the doors in transit could easily result in collision with trees or buildings at the end of the runway. Removing the rear gear doors, eliminates this problem and greatly simplifies your response to a loss of engine emergency.
There's a good discussion of take-off techniques, with and without the rear gear doors at this link:
https://www.337skymaster.com/message...read.php?t=790
I've been told MAG Aerospace has implemented this mod on all their Skymasters. For you, flying in mountainous BC, this might be a worthwhile modification. But fly the airplane for a bit and see what you think.