Would 120 LPSS and approximately 1000 life regen per second (as well as 200 LOH) be a suitable substitute for 3% lifesteal?
I wouldn't think it would be enough. Maybe if your build was super-defensive, you might be able to pull it off. Going by your profile, I'm assuming your trying to do some sort of LTK build. Those are doable (and can stun-lock), if that's what you're going for), But if you're going SOJ/Skull grasp, I think you'll just be too glassy with a Flying Dragon.
Mostly, I think LTK builds are better done with shields. LTK Shields are a pain to search for, but they let you get the extra defense, and allow for LS in the main hand. I snatched up a real nice -3 to LTK shield for my Monk recently and have been debating trying to get an interesting set of LTK gear if I ever score some serious cash.
Anyway, to give a comparison point... I was able to play on MP-10 with only 100K DPS with about 5% LS, 500 LoH, 62 LpSS, and 500 Life Regen. I used a high-mitigation build (almost 20:1 mitigation, I think). If I wanted to replace that LS, I figure I'd need another 4000 Life Regen and 60 LpSS. I'm going to guess your build won't get you anywhere near the mitigation levels I was at, but I tanked a lot of things and maybe you'll be able to do better with stuns/kiting, etc.
If you're attacking faster, using Spirit on crit attacks like quickening to generate spirit for more LpSS, and get a ton of mitigation, and use a defensive build, maybe you'll be able to get away with less. Give your build a shot on lower MPs first, even if it's with less than wonderful gear, to see what your limits are likely to be. Whatever you're doing, there's probably an MP where it works and it's fun.