The most important things you will need is an RB25DET transmission and oil pan.
You have to modify the 25's oil pan so it will fit the 26. The 26's front differential and axle go though the oil pan. The 25's transmission is used as it's a RWD transmission where as the 26's transmission has the transfer case for the front diff.
Swing over to our RB forum and search around a little. You can use the flashing red search button at the top of the page to help you on your way.
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As far as the 26 being the most reliable, maybe only in the sense of it being built very well to handle the abuse for racing. The 20's and 25's are reliable as long as you keep regular maintenence going on them.