I got a 74AC240 to use as a driver for an IRF510. However, the output of the DDS is fairly low. I was going to use a comparator to convert to a 5v square wave, but was having trouble getting it to work. I think the issue is that the LM399 I pulled out of the junk box isn't fast enough :/
I then tried making a Schmitt trigger out of an op amp I had laying around, but it wasn't fast enough either. One I tried was a bit faster, and if I got the source down to 1 Mhz it sort of worked.
Then I tried the DDS buffer to directly drive the '240 - success! The buffer distorts a bit, so the signal out of the '240 isn't that great, either. But I can clean that up with my low pass filter. I'm measuring about 400 mW into a 50 ohm load when I use 5 volts on the '240. I'm using a 12V source for the buffer and the Arduino's 5V output for the '240.
I seem to be running out of breadboard space. Hopefully the IRF510 stage won't take up too much room. Once I have something together that works, will see about moving the PA stage out to something more permanent.