I'm looking at a purchasing a great used 155 gal bow front that was a salt water tank for 7 years. Will I have any problems chemistry and residue wise converting this tank to fresh water?
No you won't. If there is any salt residue in the tank just give it a good scrubbing with a white vinegar and water mix 20/80 should be strong enough. Then rinse it well.
You could also soak it with a mixture of bleach and water in order to kill off anything that might be harmful. Just make sure you then soak a dechlorinator solution in it afterwards.