LOL, i think we built different transmitters!! i built the one by Kyriakos Kontakos. 2 high power transistors instead of 4 smaller ones. sorry my mistake!
I just finished this project as well. 20 or even 18 guage solid strand works very well. I used coils taken from a dead CB radio and modified them a bit to get the correct turns. Works awesome, coils dont even heat up.