I've done it with and without the ring gear tool. First, you will save a lot of time and labor if you have the ring gear tool. Also, if you don't have access to air tools, the ring gear tool is essential, IMO. You need a way to hold the cams when the cam gear bolts are torqued. If you have the tool, you are using the chains to hold the cam gears in place while you torque the bolts. If you don't have tool, you will need to go through the extra work of removing the upper plenum and valve covers so you can put a wrench on the flats of the camshafts to hold them in place. The ring gear tool also allows you to properly torque the crank pulley bolt and allows you to remove it, again, if you don't have access to air tools. I actually bought mine through a Suzuki site, as the Suzuki Equator is the sister of the Nissan Frontier. When I purchased it, it was $100 with shipping. Last time I checked, the tool was around half that price, but I no longer have the link to the site.
If you haven't purchased the RTV sealant for the cover, I highly recommend Permatex Ultra-grey rigid high-torque RTV #82195. The stuff is very similar to the factory sealant and much better than the black or red sealants available.
You can get it at most auto part stores:
http://shop.advanceautoparts.com/p/perm ... nt=7160239