Double jointed fingers and arms sound like a good solution.
My 7045 has had "windows' cut through the side of the mudguards to give better access/ vision. They are about 90mm high by 190 long just above cab lower frame, cut with an angle grinder. Covers are screwed on.
Bigger window would be easier to work through.
Taking the floor up gives great access but its a lot more work. If the brake lines are badly rusted then replacing them with the floor up is a lot easier and gives opportunity to get at anything else that may need painting or cleaning up.