Pat: Think you got the direction of your subtraction and addition mixed up. The addition or subtraction assumes a commensurate increase or decrease in draw weight and arrow length. I.e., 50#@28 is 53# at 29, etc. Too, the longer arrow will have a dynamically softer spine. Thus, he would need to increase static spine as draw length increases to compensate for the increased draw weight and reduced dynamic spine of the longer shaft.
Regardless, Dorado, a .340 spine is equivalent to about 93#. Even if you have a fair amount of weight on the front end, and the shafts are full length, they're going to be on the stiff side for your bow.
If you go with a point in the 125 grain range, a 11/32 POC shaft spined about 65-70# should work, give or take a little. Would be a good idea to get a test kit starting at 60-65, through 65-70 and 70-75.
Another reason you don't need as much spine with the wood shaft is that it is larger diameter than the carbon shaft, which is probably 5/16 in diameter or smaller. The effect of the larger diameter shaft is the same as building out the side plate. It holds the center of the arrow further from the center of the bow, thus it needs to flex more to clear the bow cleanly when shot. That means the spine has to be reduced a bit so the shaft will flex more easily around the riser.