For defensive Steelix, Gyro Ball is nice for the power, but Heavy Slam seems more appealing for the greater PP (relevant against Sub users like Uxie and Articuno), much better damage against Granbull, and doesn't miss out on any notable 2HKOes on Gyro Ball targets, which improves (or at least doesn't worsen) Steelix's consistency in checking threats. In most cases, if one is confused about weight, it's usually better to EQ an opponent anyway, though a list of Pokes hit harder by Heavy Slam than EQ, such as Kangaskhan and Sawk, would be useful (namely neutral Pokes of 80 kg / 176 lbs and below, refer to Bulbapedia coolking49).Just... Just use Gyro Ball. In issues a Pokemon who doesn't get hurt more by it is a very specific case and usually you can EQ them. Iron Head is nice for the no LO recoil, but it's a little lackluster and Heavy Slam is just... I hate Pokemon weight.
It's probably stupid but I would put AV in OO since it CAN work, it's just half assed.
Offensive LO Steelix can make use on non-LO recoil Iron Head or net more KOes with Gyro Ball than with Heavy Slam, so Heavy Slam doesn't have a place here.
AV Steelix is complete ass, mostly because of poor damage output, lack of any recovery, and inability to use support moves.