I finally got the 1CC using the 2C plane. I was a real bitch for me to do though. Everything is a bit hazy, but what I do remember:
Stage 1 - Grabbed the secret bomb.
Stage 2 - Used a bomb on phase 2 of the boss.
Stage 3 - Used a bomb on the miniboss. While I could get through this section without bombs, I started using a bomb preemptively so my runs would have a much higher chance of at least making it to stage 4.
Stage 4 - Things got hazy from here on out. I think I died once on the boss...?
Stage 5 - I didn't have napalm at the miniboss, so I used bombs to kill him and get the extra life. I definitely went into the final boss with 2 lives and maybe 1 bomb on my current life. Died once and had 1 bomb left when I beat him.
I tried 1C immediately afterwards and got a 5CC. I was surprised how many boss attacks you never see with 2C or how some easy sections become way harder. I sincerely doubt I could get a 1CC with any other plan than 2C.