I'm looking at the 1.3 version from Frodo.
Type B'FUNGUS during play to enable cheats.
The active ones are 'J' (move far left), 'K', (move middle), 'L' (move far right), '-' (level select, accepts 1-9).
There was a set of cheats whose code remains, but no references to them.
They are the better ones, so search for this sequence:
ED 8F F3 8F F9 8F
replace ED 8F with E5 98 (now 'J' increases helicopters)
replace F3 8F with EE 98 (now 'K' makes you invulnerable to bullets and collisions with the other heli, but not balloons, bombs, or crashing)
replace F9 8F with 2A 99 (now 'L' does... I'm not sure. It looks like it might display something. It appears to be used during save/load, but AppleWin won't let me press ESC anymore, once the debugger becomes active).