I really don't think it would make a BIG difference to subsitute another conversion compay in it's place like Mark III or PrimeTime or what ever. The main question is the info like your signature states; 99 Ram Van 1500 LWB Conversion by Legend, 360 Magnum / TV / VCR / Bed / Full power / AM/FM/CD/Cassette / 3.55's.
The only conversion company that gets just a little more for it's value is StarCraft.
Have you tried Kelly BlueBook (KBB) too? NADA tends to run higher than what the general public often pays anything for. Kelly tends to be the fair market value that people are will to pay for.