I played one year (1985), so here's what I can tell you in my case, and my Oregon bud (who grew up in a wheel chair, so he obviously never played, though he's walked now for years) and I were talking last night.
Back then, nobody - and I mean NOBODY - worried about head injuries.
You feared two things:
1) knee injuries
2) paralysis
And even then, Darryl Stingley was the only point of reference any of us had (Chuckie Mullins and Mike Utley were years in the future), so that wasn't really a big fear in high school, the knees were.
We were taught to stick that helmet right into the guy's ribs or go low for tackle and take out his legs. Almost everything we were taught with that helmet was explicitly forbidden on the little sticker on the back of it. But here's the thing - that helmet was a feeling of invincibility. You PREFERRED to involved your head because hitting the ground with your body even in pads hurt like hell, but hitting the ground head first took a shot really only NFL guys could give (for the most part) to actually hurt you. I have NO DOUBT that if a little guy like I was (5'7", 127 lbs the day I graduated high school) felt invincible that much stronger, tougher, bigger guys than I did felt the same way (after all - they were hitting me since I was a slow running back but too small to play offensive line).
We had one guy - a friend of mine (now a principal, which is hilarious as we graduated together) - he was our punter his senior year only. He was a hefty guy, but he had a lot of leg, and the coach found out and got him to play. In our last game of the year, we were 20 points ahead in the second half when our douche bag of a coach (and he was, folks) called a fake punt. Our lumbering punter took off and got the first down. When they tackled him by piling on, his leg did the Joe Theismann back snap. Guy still walks with a bit of a limp despite losing weight and looking good at our age.
(Side note nobody cares about: former Alabama player Will Friend's father was my fifth-grade P.E. and homeroom teacher; he's the first guy I ever sat and watched game film with although I'm sure he wouldn't remember me 40-plus years later).