Suzuki: Noisy, ? risky, 4 wheel drive low in amphibian, suzuki jimny, wheel drive suv

Question
I have Suzuki Jimny 2001/2002 low mileage (16K) transmission fitted into a watertight glass fibre boat hull,the same dimensions as the metal Jeep body, as is everything else in road use the same as the original vehicle.  The builder forbids any use of the 4 low or high drive state (transfer box) on hard ground and the problem is, I don't want to risk wrecking hubs/diff/transfer box when exiting the water on a concrete slipway.  This is of course in conflict with the requirement of 4 wheel drive state on a steep ramp, which may be 20 or 30 yards before it levels out.
How dangerous is it to the mechanics, to drive 20 or 30 yards in a straight line, especially if in this vehicle it is quite audible from the front - the discomfort/imbalance of the drive trains?  (The 2 wheel drive high recommended "as soon as out of the water" is unsuitable practicably, as the rear wheels are not touching, as the front wheels bump onto the slipway on exiting water, and instruction manual insists one stays in 4 low or 4 high while driving the 'jet' turbine prop until one touches the riverbank/slipway.  Even if there is no side current (unlikely) it is difficult for an average person to change, at the instant Jeep lifts the nose out of the water, into the recommended 2 wheel drive, which in a loaded vehicle would often start slipping even on dry concrete.)  Can you explain what is actually happening?  and why a fairly recent model, post millennium 4 wheel drive SUV by a good manufacturer cannot be allowed to do what a simpleton like myself, without prior knowledge would expect a 4WD to do.  (Designer insists that all "parttime" 4WD's should NEVER drive on road surface on 4WD unless it is slippy or soft.)  Thank you in anticipation.

Answer
I suspect that the major issue would be the possibility of overstressing and cracking the fiberglass body, not damaging the drive train.  I suspect that leaving it in 4wd until all four wheels make contact would be acceptable.  This is primarily because there is no provision for "slippage" in the Suzuki drive train.  Wouldn't the first five or ten feet of a boat ramp, especially when wet be somewhat "slippy"?
scotty