MGD, I have measured several of my older Ultras back in the day and I got anywhere from 50-150lm brighter than the stock Sylvanias these trucks run with. Of course, it was not a scientific test and did not factor in bulb age, voltage, etc. I was just confirming my suspicions.

OP, I think you would be pleasantly surprised by a retrofit. You could do it for about $150, but the more you spend, the better components you'll get.