Chris, I have to start with the most obvious issue at hand, the fact that you believe your drugs are uncut and pure. The chemists in Marseille or Sicily or wherever-the-fuck are probably not making 100% pure, uncut Heroin. The only instance in which you can absolutely say that you have pure drugs is by witnessing them being tested in a professional setting with your own eyes. As a general rule, street-dealers do not sell pure drugs. It is just not a thing.
I believe you might have access to fairly pure drugs, so we can proceed with that assumption. While I think it's great that you have Naloxone (Narcan) on hand, it's not likely that you will be able to administer it in the case of overdose. There is a reason you don't commonly here of users administering Narcan to themselves. If you actually administer an overdose to yourself, you are likely to cross the line into lethal respiratory depression before you even have a change to reach for the Naloxone.
The dosages that you have mentioned should be perfectly reasonable. I'm not sure what kind of quantities you're working with, but if you're looking to go the safest route possible, I would suggest modifying your dosage and administering it orally for the first time. This is the smartest and safest way. You will be working with a slower onset and you will have the opportunity to make better decisions in that time should you happen to overdose.
You mentioned that you are looking to try several different ROA's, so how about being smarter and more responsible than "those other guys" and try your drugs orally for the first time. You seem to understand how to use Opioid equivalency tables, so once you ascertain a good dosage orally, you can proceed to possibly doubling that dosage and attempting an ROA with a quicker onset, like insufflation.