Assembly / Disassembly
Go to Amazon.com and do a search "Gun Digest Book of Firearms Assembly Disassembly" . It comes in several books.
Look for the specific book Part IV Centerfire Rifles. Currently $15.99 new.
It has a chapter on complete tear down of the 742, which also covers the Model Four, 74 Sportsman, 740, and 7400 series.
With pictures and text. And tips on reassembly.
I inherited my dear father's 7400 we bought in 1988. He cleaned it and lubed it well. Runs perfectly. Probably just short of 500 rounds, maybe less, still like new. Not a match grade rifle, but I've shot deer running full tilt downhill into the aspen groves. It'll hit a deer, both dad and I testify to that. I still miss hunting with you, Dad.
The plastic cover that goes over the ejection port may break or come loose. Remington considers it an expendable part, you simply buy a new one for $7 and replace it.
If you handload, the gas circuit is made for full loads. Doesn't run well on starting loads, or pansy powder puff loads. Start low and work up, but only load 2 or 3 rounds at a time. Test them to see if they cycle the action before you load too many.