The Remington Model 7400 extractor is a semicircular shaped part made of spring steel that is held in its correct location with a rivet. This rivet needs to be properly staked in place and blended with the outside diameter of the bolt head.
This is a job that should be done by a competent gunsmith that has the correct equipment to do the job properly.
The model 7400's extractor was changed from the earlier model 742's which as noted above was riveted in. The model 7400 has a snap in extractor - no rivet. I replaced mine by inserting a curved tool (I modified a small thin screwdriver by bending the tip) through the magazine well under the extractor to pull out the remainder of the old extractor, then snapped in the new one. The new extractor cost 20 dollars (with shipping and tax) from Remington.
Best left to a gunsmith
Yes they are interchangable.
The weight is 7.5 lbs
Contact the Remington Custom Shop
You can request one from Remington for free at their web site.
100-425 dollars
$500
Yes, The receiver pins are the same as the Remington 870, so any stock that will fit the 870 will fit the 7400
If you mean a Remington 514 series bolt action rifle, the extractor is L shaped, and pulls straight out from the side of the bolt. If not careful you will lose the extractor plunger and spring. I would take it to a gunsmith- getting the new one in requires fitting.
250-450
100-400 or so
Age.