To give you a little more help and save you some money I'd suggest buying the timing chain parts online. Courtesyparts.com is good as you can select which item you need. Other sites like those listed below will only give you the basics, I believe, like front main seal, tensioner, lower guides and bracket. You will need 2 o-rings and I'm not certain if they are included. The reason I'm telling you this, it just cost me $19.62 CAN at Nissan for one o-ring when I could have bought it online for $4. The only problem is shipping to Canada which takes time and if shipped via UPS or FedEx it would be expensive.
http://www.autopartsworld.com
Search Google for
Sentra Timing Chain Kit and you will get a similar list of retailers using the exact same search database and prices.
Ultra Grey Sensor-Safe RGV Gasket by Permatex is what Nissan uses when reinstalling the front cover housing and that can be bought at WalMart for $6 or so. Again, you might save some money buying the supplies yourself and giving it to the mechanic. Same goes for oil and a filter.