Ok, so basically, with the Imperium of Mankind being such a technologically regressive culture with most tech being ancient and the common patterns in use by the 41st Millennium generally being the easiest patterns to mass-produce, I reckon that most current Space Marine equipment was at least beginning to enter use towards the end of the Great Crusade or during the Horus Heresy. To this end, I've used the FW Horus Heresy series and some other sources to work out just what aspects of 40k Space Marine equipment was around in 30k. Mainly this equates to what GW plastics can be used (sometimes with modification) in HH armies without breaking the fluff (being a fluff bunny I would prefer my HH forces to not be 'historically' inaccurate).

OK, so here is the evidence I have accumulated so far. Special attention has been given to the Godwyn/Ultima pattern of bolter as I would find it very useful from a modelling perspective for it to be extant pre-Heresy. Any other GW plastics I have not added that people feel would be appropriate, let me know. Additional evidence (preferably with a source and page number) also will be much appreciated.

GW plastics HH background evidence:

Godwyn/Ultima pattern boltgun, bolt pistol and Maxima pattern heavy bolter. Ultima pattern weapons confirmed in use at least by Salamanders. Ultima weapons are pre-Heresy, unknown how commonly. No evidence for heavy bolter or pistol, but pistol especially is likely.

HH Book 1: Betrayal
Held by Death Guard Marines in page background images. Pgs 124-126, 156-157, 203, 205, 207, 222, 266, 281, 284 (very clear example).

HH Book 2: Massacre
Ultima pattern Combi-flamer used by Firedrake squad Kal'sho, pg 124.
Held by Death Guard Marines in page background image. Pg 15. Likely same Marines as in images in Book 1.

HH Book 3: Extermination
None sighted.

HH Book 4: Conquest
None sighted.

HH Book 5: Tempest
None sighted.

Mk V Castraferrum Dreadnought. Extant pre-Heresy, unknown how common.

HH Book 2: Word Bearers Mortis Dreadnought image Pg 154; Legion Mortis Dreadnought entry description margin.

Indomitus pattern Terminator armour. Extant and widespread pre-Heresy, especially in Imperial Fists Legion. No Crux Terminatus though to my knowledge.

HH Book 2: Gorgon Terminators entry, description margin, Gorgon Terminator armour description.

HH Book 3: Imperial Fists Legion background information, Legion Organisation.

MkVII 'Aquila' power armour. Developed by surviving loyalist armour researchers evacuated from Mars. Completed and beginning in issue to loyalist Legions during late Heresy, probably for the Siege of Terra.

Phobos pattern Land Raider. Extant and widespread pre-Heresy, even without enclosed, armoured sponsons (FW variant). Crusader and Redeemer variants definitely post-Heresy.

HH Book 1: Legion Land Raider battle squadron; background image in campaign section.

Mars pattern Rhino and variants. Confirmed, less common use by Legionnes Astartes. Predator Annihilator and Razorbacks definitely post-Heresy.

HH Book 1: Mars pattern Rhino in background image, pg 217.

HH Book 3: Iron Warriors Mars pattern Rhino, pg 127.

HH Book 4: probable sighting of Death Guard Mars pattern Whirlwind, pg 187.

FW webstore lists Mars pattern Rhino doors in Legion section.

Ultima/Incaladion/other sub-patterns of Stormbolter. Probably post-Heresy (Scouring or early Age of Imperium).

Codex: Chaos Space Marines, 5th Edition: suggests the combi-bolter was in use amongst Loyalists until post-Heresy.

Monocore Ryza/Mars pattern plasma weapons. Sunfury pattern pistol confirmed, Ragefire pattern gun and Comet pattern cannon likely too.

FW webstore: Anakatis Kul Blade Slaves wield Sunfury plasma pistols; Tartaros pattern combi-weapons use Ryza/Mars pattern plasma weapons.

Ultima pattern meltagun, Fury pattern Inferno pistol and Maxima pattern multi-melta. Barrel type is definitely in use, unknown for full melta pattern, but very likely.

FW webstore: Tigrus pattern combi-weapons, the melta component has a barrel matching the Ultima pattern meltagun, rather than the Primus pattern meltagun. True for both the Legion Combi-weapon pack combi-weapons and the combi-bolter based combi-weapons with the Tartaros pattern Terminators (the latter shows more of the weapon showing it to be similar to an Ultima pattern meltagun).

Heretic pattern flamer and heavy flamer, Ignis pattern hand flamer. Unknown, probable.

Mars pattern Grav pistol, gun, cannon. Unknown, probably post-Heresy, due to the graviton Imploder only just being extant at the beginning of the Heresy (the Imploder being the precursor to 40k Grav weaponry).

Soundstrike pattern missile launcher. Unknown, research pending. Probable, basic design.

Mk VII Mars pattern Lascannon. Unknown, research pending. Probable.

Mars pattern Land Speeder. Discovered post-Heresy. The Great Crusade version therefore currently has no available model (FW will likely produce a model based on the classic GW Land Speeder).

Imperial Armour volume 2 second edition: Land Speeder background information, pg 148.

Phobos-Lucius pattern Drop pod. Confirmed, main Drop pod pattern in use.

HH Book 1: World Eaters Drop pod, pg 205.