Head: 50th Dusty
Helmet, visor: Vintage Battle Gear
Everything else: 25th Flash
Flash was one on my first Joes that I got as a kid. I remember liking the color scheme and the weapon. Flash would often man the top of the APC after the cannon got destroyed.
The official 25th figure, though dated, is still dead-on accurate as far as sculpting details. For my custom, I kept the base body. I updated the head to something more proportional and gave him a vintage helmet and visor to bring him in line with the other Joes. After that, he got painted to match the rest of the team.