I mean maybe you haven't played ball, but that doesnt matter. Power is different from strength. Power is all about how many muscle motors(fibres, crossbridges, etc.. whatever you want to call them.) you can recruit in a burst. Power if I want to bastardize it more, is Strength x Speed. Now if we go back to the boys you were talking about, linebackers and especially linemen are big boys so they are strong naturally from playing the position or should get to be because of their weight advantage and leverages. They mostly need to learn to toss their weight around faster, but of course they should still lift weights to get the other factor of power being strength up to par with the enemy teams.
The runner thing idk where you are going with. Ever see a 300lb dude run a 4.4 40? If he could I doubt you would stand infront of his big ass because you'd be mowed down. So if some lightweight is running, no **** he wont mow you down haha.
You'd be surprised you can buy a pulley system online for like $150 that can attach to the power racks and wont take up any room. Teaching a squat is much easier, but I still rather not put a bunch of load on someones back if there are better ways. I think the load is probably not a problem, but football can be rather harsh on the body and I've worked with and been a youth athlete, so when I look at them I want them to be able to play pain free and injury free as long as possible. Some of these HS coaches beat the **** out of these kids and they can't even play college properly let alone Pro, which pisses me off.