I've played with a few versions of a generic '70s-style Iommi preset over the years, and I've posted a few versions to the Facebook-based AmpliTube preset group, which you could find there, though I can also explain my general approach.
IMO, the core of the Iommi/Sabbath tone in the '70s was a Laney head boosted by a Dallas Rangemaster treble booster (modified for, it seems, a fuller range boost). In theory, you want P90 pickups, but humbuckers will get you close, I think
The early Laney heads are said to have been closely modeled on contemporary Marshall heads. Your best bet here in AmpliTube is the JH Gold, technically modeling one of Jimi Hendrix's JTM 45/100 heads (and, so, no bad thing in itself!), so the circuits and tubes are a bit different from a standard #1959 Superlead, and perhaps a bit different again than a Laney LA100BL ... but there's nothing closer in AmpliTube, and this will get you "in the ballpark".
Online info suggests that, back in the day, Iommi plugged into the Bass channel on the Laney (i.e. channel 2 "Normal" on the JH Gold) and dimed everything except the bass, which was was turned all the way down. That said, a video from Laney on YouTube looking at Iommi's live rig from the final Sabbath tour, using the reissue LA100BLs (
https://youtu.be/g4sSERzW6Ew), says that, at that point, the reissue amps were being run with the EQ controls "pretty much" flat, but the gain "turned up full". So ... your mileage may vary! But you can see in the video that the Laney "Bass" channel is what is being used, so definitely turn the "Normal Loudness 2" control on the JH Gold all the way up
and then put everything else at 5, at least to start with. Trying turning the bass down, as needed, and the treble/mids/presence up as needed.
Then, the Treble Booster from the Brian May pack has a setting that is intended to emulate May's '70s Rangemaster, though you may find the '80s or '90s setting on that stomp model as good or better for approximating Iommi's modded Rangemaster tones. I tend to put the Star Gate from the Brian May pack as the first stomp in the chain, then the Treble Booster after it, because a treble booster into a cranked amp is
noisy.
(A lot of the Brian May presets start with a Star Gate for similar reasons, I think!)
With regard to cab/speakers, there is much online speculation about what Iommi used at various points in the '70s. The recent reissue Laney LA100BL has a matching 4x12 with Celestion G12H 75Hz speakers. These
may (or may not) be more similar to AmpliTube's "Brit Anniversary" speaker models than to the "Brit Green" speaker models (probably based on G12M speakers); what original Celestion speakers sounded like new, sound like now after 40 years, sound like when they are reissued, and sound like when they are reissued with a little more care can all be different things.
In
any case, Laney cabs in the early '70s may have used a variety of speaker types, depending on what was most available, etc. I've heard that Fane speakers (perhaps similar to AmpliTube's "HiAmp" speaker model) were sometimes used, and perhaps Goodmans Audiom speakers (which may or may not be modeled by AmpliTube's "Brit Alnico S" speaker model). Ultimately, you may want to play with any of those speaker models, or combinations of different speaker models, in a "based on vintage Marshall" cab model. I have often used the 4x12 Closed 25 C model cab, swapping around speaker models as seems good, though I've now switched to the Satch Green cab model (which, IMO, sounds great with or without its stock speakers).
BTW, the Sabbath records recorded in the UK may well have used Neumann mics (e.g. AmpliTube's Condenser 67 or Condenser 87) to mic the cabs (certainly more common in the UK in the early '70s), while Vol. 4, recorded in the US, may well have used SM57s (then more common in the US).
With that info, you should be able to dial in a plausible Iommi tone for yourself.