9 times out of 10 the barrel is already set for 3" shells so check your barrel, if it states 2 3/4" or 3" in magnum receivers, then thats all you need to do !
It would not run $300.00 to do the convertion, if it did I would suggest just picking up a new 870 express!
RON KONTOWSKY
DEAN`S GUNSHOP II
http://www.deansgunshop.com