DATSUN ENGINE PARTS SOURCES for 2010
While I can't speak for Nissan I doubt they have a factory devoted to making parts for motors that haven't been produced since 1983. The Japanese are experts at outsourcing parts (examples are Nabco, Tokico, Hitachi, Lucas, ) nowdays they likely have manufacturers in Asia making parts to Nissan specs. Nissan parts are factory quality with the expected high prices.
Beck Arnley has been a parts distributor since 1914, they don't manufacture parts. Due to their high quality and Nissan-like prices, I've always suspected they import parts from the same sources as modern day Nissan. A timing chain set of theirs I purchased in 2006 was labeled "Made in Japan", a welcome surprise. A main bearing set I bought was labeled "ACL" of Australia which is highly respected. I would make Beck your first choice after the dealer.
The american company Federal-Mogul of Michigan owns nearly every other aftermarket company: Sealed Power, Speed Pro, Fel-Pro, Champion, Carter, Ferodo, Wagner, Moog, Wagner, National, Precision, Abex, Anco, and supposedly Crane Marine. This gives Federal Mogul a huge inventory to draw from for Z parts. However, they declared Chapter 11 in 2003 due to asbestos claims. Since the 2009 meltdown of American car companies, you can bet that L-series parts are becoming less of a priority for them. Buy 'em while they last.
Borg Warner is a niche company nowadays and concentrates on high-quality electrical items such as voltage regulators and ignition parts. Their distributor caps and rotors use the coveted brass contacts and I bought a 240Z mechanical voltage regulator a while back which was very high quality. Borg-Warner doesn't support T5 transmissions anymore, they sold the rights to Tremec in the 1990's and won't even respond to questions on them.
DANA and CLEVITE
Dana is the parent corporation of Clevite and in March 2006 declared Chapter 11 bankruptcy. Napa used to carry Dana parts which consisted mainly of bearings sets and pistons parts. Clevite made an OEM L-series camshaft I bought from Black Dragon Auto a few years ago.
JC Whitney is just a catalog company with about a zillion suppliers, they don't produce or manufacture anything. When you buy engine parts, headers, tools, performance parts, you're just getting the aftermarket brands listed above. No secret underground line of parts...trust me.
My Personal preference of new internal Z parts
MAIN BEARINGS: use factory Nissan. The price is good the tolerances can be trusted. My dealer: $50.
ROD BEARINGS: Nissan are pricey. Beck Arnley gets the nod here. My auto store: $28
PISTON RINGS: I have used Beck-Arnley three times with good results, $50. Nissan and Fed Mogul are $$$.
HEAD GASKET: For non-turbo engine I think Fel-Pro is great, easy to remove too. My auto store $20.
TIMING CHAIN: Several companies make replacement chains. I would again go with a Beck-Arnley full set for $79.
MISC ENGINE GASKETS AND SEALS: Fel-Pro and Beck Arnley make a great general gaskets. Rubber seals should be Nissan, always.