Hello and welcome to justanswer.com
You are correct that there are 4 timing chains. Two that go from the cam to crank and 2 that go from cam to cam on each side. The total labor to replace them is about 15 hours. The chains are different before and after the build date of 5/14/01. There are special tools that are required to do the job. You will need the cran lock which goes in place of the crank sensor and the cam locks that hold the cams on the flat spots. If you are going to replace the chains I would recommend replaing all chains, guides and tensioners. Also keep in mind that depending on when the chain broke there may be engine damage.
You really can't do a compression test with a broken chain. You can do a leakdown test to see if there's a bent valve. I can send you the procedure in the next post. It's a lengthy procedure so it will take a few minutes to upload it as I need to convert it to pdf file.
Timing chain 1
Timing chain 2
Timing chain 3