Actually, I have a connection over here in Japan that will order and ship stock parts. She works at the hobby shop here on base. You tell her the part and the motor type. She looks around all the usual local shops for who has the best price. She's also a certified mechanic, so you can't BS her.
As far as easy to change goes, Once you've modified the front split cover, the timing belt, tensioners, waterpump and cam gears are easily taken on and off.
The head gasket is pretty straight forward. Basically the same as any over head cam engine. Just put the motor at TDC and remove all the bolts securing the head to the block, you just have to watch out for the 3 10mm bolts on the corners. They need to come out first.
There is a ton of good info on
http://www.Skylinesdownunder.com
WD