Hi:
Sorry to have taken so long to answer but just didn't get the time.
I find the comments so far to be very well thought out.
My best advise would be to treat the first test flight exactly as any other flight, bearing in mind that there is a remote possibility that the airplane could be out of rig slightly due to what ever caused the damage.
So what we have to contend with here is flying a Beech 18 very carefully considering all the work performed on it.
The B18 is a very straight foward airplane and exibits no adverse flying characteristics that will suprise you, if you keep the sucker going straight down the runway on take off and climb it at the recommended a/s I canno't imagine there being any control problems that canno't be dealt with to return for a landing.
Take one of the engineers that worked on it with you as a co-pilot as they can cope with any mechanical problems better that the guy flying it.
One last comment, if there is going to be any real control problems it should show up just after becomming airborne.
Should there be "any " doubt in your mind that you "may" be unable to maintain control as a/s increases, abort the take off even if it may result in wrecking the thing again.
It is better to wreck an airplane and walk away from it than kill yourself because you tried to save the airplane.
I hope my comments help, as it is difficult to advise someone by offering suggestions that may not work.
The B18 is a great little airplane, just keep it on the center line on take off and landing.
By the way the B18 is a superb airplane on floats, I flew one for two seasons many years ago, also the Volpar Tri Gear B18 was a great little machine, only drawback was the slow gear retraction and extention.
Does your 18S have the walking gear in it?
Chuck E.