GMC / Chevy C4500 C5500 TopKick Kodiak 5 speed to 6 speed Conversion

Wondering if anyone knows the answer to my question ? So, I am aware that in a 2006 - 2007 GMC / Chevy C4500 C5500 TopKick Kodiak you can replace and reprogram (with a TECH2 and maybe other software etc...) the TCM with a 2008 2wd or 4wd VIN# and you'll go from a 5 speed to a 6 speed transmission instantaneously, nice and easy. But on the 2003 - 2005 models you can also go from a 5 speed to a 6 speed transmission as well, but you have to purchase a kit which range online from $1,500 to $2,500 depending on who you want to purchase it from. The kits contains a 6 speed valve body and a TCM. Now my question is can I just purchase or remove a used 2006 - 2009 6 speed valve body, and swap out the solenoids from the 5 speed into the 6 speed valve body, which I believe I read somewhere that you have to do this for it to work ?, and then just reflash/replace/reprogram the TCM with a 2008 2wd or 4wd VIN# or purchase a used 6 speed TCM ? This way the costs should be a lot less and I was thinking of purchasing a 6 speed back-up transmission and using the valve body, in case mine ever goes. Any feedback would be appreciated.