Chris- Dave's coach is a 2001; thru 03 model year the rigs were wired w/relays in prefab "VEC" modules located in the same place as your Vansco modules.
1997 thru 00 coaches have a step well cover that hinges up to cover the front panel covering the VECs. It wouldn't be practical to install this handrail on those.
01-03 coaches have the VECs and a fat wire loom from them across the top of the firewall to the left. Dave checked this out before taking the handrail project on and decided it was going to work. There may be some adjustment to the tie-downs for the wire loom needed at the top end on these VEC equipped coaches, but the rest appears to be a drop-in install.
04 (and maybe 05?) rigs have the wood sound board on the inside surface of the metal firewall like the older rigs, but Vansco modules and smaller wire looms. Also next to the Vansco to its left is the SmartWheel module on models so equipped. The rail mounts to the left of the SW module; same mount location for the lower plate as shown in Dave's photos.
06 (and maybe 05?) rigs have the metal-only firewall with a sound material laminated to the front side. Same wire loom routing as 04 rigs, so same mount except thru-bolt to the metal firewall instead of screws to the wood sound board.
Apexes have Vansco's mounted to front of lower front metal bulkhead, and a HydroHot radiator assembly mounted where the Vansco is on earlier coaches. Because the wire looms are moved tot he outside, the landing point for the upper handrail bracket is simpler and more free as far as minor adjustments. Also the lower plate can be moved freely to allow individual preference because the battery disconnect switch is moved to the battery compartment.
SE's also have the battery switch in the back, and have easy location of the lower plate. One word of caution- run the step cover out all the way to locate the loser plate (and upper plate) or you run the risk of placing where the step cover won't open properly.
On the 06 and later coaches (maybe 05's?) there is a hole in the metal firewall approx. 20.5" up from the floor and 25.5" left of the right wall of the coach. There may be a 3/8" bolt in the hole holding a support for the dash, or the hole may be empty. My coach used this hole (mine had the dash support) and 3/8" bolt to hold the upper plate to the firewall. The lower plate mounts with self drilling/tapping screws to the metal stairwell side wall.
One last piece of work to complete the installation- you have to trim the upper lip of the VEC or Vansco (or for Apex- HHot) panel in front of the copilot to allow the upper end of handrail to die below the dash where is is inconspicuous. I used a 2" hole saw to make a neat round cutout for the vertical section of pipe at the top of the handrail, then a Dremel Multi-Max
to taper a slot from the round hole to the rear edge of the formed plastic panel. You can use hand tools for the same task. After installing the handrail and trimming the panel, you hold the panel below the sloped part of the handrail and hook the right hand part of the upper lip behind the bar, then work it up into place. This is the only inconvenience I've noticed (versus pulling the panel sort of straight out, maneuvering it sort of straight in). If you cut the hole saw hole leaving about 3/8" of upper lip remaining, the upper lip area becomes flexible enough to do the maneuvering. Your 04 will be easier than mine as the panel is shorter left-right (i.e. you have two pieces where the 06 & later (and maybe the 05?) have a longer one piece panel setup for access into this area of the dash).