thanks for the links kev!
I don't like the idea of a different stock, I really like the idea of spacers.
I did some more research tonight, and pulled the 3 guns I'm interested in making longer down and pulled the back end off...
my remington 870 is a synthetic stock, and it's hollow. The butt pad slips into the butt itself, and there's no way to put a spacer that isn't custom made in. I'm not entirely sure what I could do here short of getting a new stock, or a custom fit spacer...I don't really like the wrap around type of recoil pads.
my remington model 5 is the easiest. solid wood. a spacer shaped from stiff rubber or wood would be fantastic in this case.
my tikka t3 lite has support inside the butt that would support a rubber spacer, but they might have to be fitted inside the stock for a small part...tough, but not impossible.
as it turns out, all 3 stocks are the same length...it would be really awesome if they would all be able to be solved with the same product....