500 USD or so.
No, they are readily available.
100-400 USD
Yes, The receiver pins are the same as the Remington 870, so any stock that will fit the 870 will fit the 7400
Check this table for the answer: http://www.remingtonsociety.com/rsa/questions/barrelcodes
300 to 500 depending on condition and accessories. The rifle can be replaced for under $500
$500
DO NOT TRY THIS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! You will cause great bodily harm and damage if you attempt to do this.
250-450
100-400 or so
Remingtons are dated by a letter code on the left side of the barrel, not the Serial number.
No. Minor difference, may be adapted to fit. Sights from the 740 would be a closer match. Check with Remington Customer Service- but the model 74 was only made for a very few years.
The Remington Model 742 was made from 1960 until 1980, and it was replaced by the Model 7400 in 1981.