Yeaaaaaah
That's going to be tough. Really tough.
It depends.
The thing with space marines is that they tend to be inversely stupid to age and experience.
With the exception of madmen like Black Templars the older a Marine the more likely they are to just grit their teeth and get on with it.
Now we do have some things going for us.
1. We're certainly not going to be against their religion assuming they're keeping to relativly standard Blood Angel views
2. They're going to be a bit more accepting of deviation (they're scaley after all ect.)
3. We're proven to be tough and anti chaos
4. We have demonstrated our strength by nomming Garkill and Valinor in the space of a year.
5. Most importantly we have Julius and Horatius two Segmentum level legends thanks to Horatius's Crazy skillz.
If they're going to get angry cause of the Quartok I fear they will simply have to grin and bear it cause as it stands while they could possibly beat us on the ground we could massacre their fleet (700 imperial era capital ships vs our Dark Age battle ships.)
Though negotiations maybe frosty.
In any case I'm not giving them any STCs we can send them vast amounts of Imperial era stuff for cheap, but no DAoT stuff till much much later.
I don't think such a blanket ban is really necessary. We're working on a new line of Astartes-grade power armors which should be safe to trade - the Blood Dragons aren't going to be trading that away, and the rest of the Nest lacks the Black Carapace to use the new patterns of armor. The lascannon-Hydra isn't exactly revolutionary, so it should also be safe. Heck, I think there's even a few Impaler variants we only discovered after the Fall of the Imperium, which would round out their arsenal without actually adding any new toys like neutron lasers or stable plasma weapons.
I'd rather not consider giving them anything just yet, but I'm pretty sure they have the black carapace. Its artificial, but unless they lost all their apothocaries and medical records (a near impossibility for blood angel descendants) or they're so mutated they can't implant it anymore which would have certainly had them censured long before the Imperium ended then I think they can still make it.
Personally I'd rather send them something much nicer and bigger.
Ships.
Capital ships specifically they have 700 and we can make Imperial Era battleships in a mere 12 years.
I say we send them a few hundred Imperial era crusiers to make them a primir power in the area.
Even better for us it'd be cheap as chips.