I did a post once about the HPP helmets, here's a visual. These predate a lot of the HPP Hot Toys figures so the models aren't as great looking
The helmet variant used by each armor:
Mark 8 - Mark 7
Mark 9 - Silver Centurion
Mark 10 - Mark 7
Mark 11 - Heartbreaker
Mark 12 - WM2/IP/Hot Rod
Mark 13 - Mark 7
Mark 14 - Striker
Mark 15 Sneaky - Sneaky
Mark 16 Nightclub - Nightclub
Mark 17 Heartbreaker - Heartbreaker
Mark 18 Casanova - Mark 7
Mark 19 Tiger - Mark 7
Mark 20 Python - Silver Centurion
Mark 21 Midas - Mark 7
Mark 22 Hot Rod - WM2/IP/Hot Rod
Mark 23 Shades - Shotgun
Mark 24 Tank - Heartbreaker
Mark 25 Striker - Striker
Mark 26 Gamma - Striker
Mark 27 Disco - WM2/IP/Hot Rod
Mark 28 Jack - Heartbreaker
Mark 29 Fiddler - Mark 7
Mark 30 Blue Steel - Silver Centurion
Mark 31 Piston - Silver Centurion
Mark 32 Romeo - Nightclub
Mark 33 Silver Centurion - Silver Centurion
Mark 34 Southpaw - Mark 7
Mark 35 Red Snapper - Red Snapper
Mark 36 Peacemaker - Red Snapper
Mark 37 Hammerhead - Hammerhead
Mark 38 Igor - Igor
Mark 39 Starboost - Starboost
Mark 40 Shotgun - Shotgun
Mark 41 Bones - Bones
Mark 42 - Mark 42
The helmet styles are:
Silver Centurion (also used on Mark 9, Python, Blue Steel, Piston)
Mark 7 (also used on Mark 8, Mark 10, Mark 13, Casanova, Tiger, Midas, Fiddler, Romeo, Southpaw)
Heartbreaker (also used on Mark 11, Tank, Jack)
War Machine Mark 2 (also used on Mark 12, Hot Rod, Disco)
Striker (aka Thumper) (also used on Mark 14, Gamma)
Sneaky
Nightclub (also used on Romeo)
Shotgun (also used on Shades)
Red Snapper (also used on Peacemaker)
Hammerhead
Igor
Starboost
Bones
Mark 42