I've built a bunch of these, using both Renesas and Exicon lateral MOSFETs, and subjected them to all manner of abuse. I had one fail, due to a leaky mica compensation capacitor (see noiseUnit speaker thread), but apart from that they've been rock-solid.
Lots of component substitution is reasonable. I like to use MELF resistors, but that's mostly just bloody-mindedness. An exception is the feedback divider. No, It won't work with cheap vertical MOSFETs.
The design is free for use for non-commercial purposes.
The 50W design is available on my Google drive
my Google drive