340 Intake Manifold Heat Shield

Finally managed to get at least one rivet out in one piece. I had to crush the head of the second one, there was no way to get it out in one piece.
The substance under the heat shield was as mentioned by MoparMike: solid as a rock ;-)

I will drill out the rest of the second rivet. Do you suggest to use a new rivet or should i cut a thread and use bolts?
I would like to sandblast the whole intake but use nutshell to be on the safe side. Have you guys done that and any hints? With this i also hope to clean out the hard carbon from the heat crossover because this one is almost blocked.
Thanks a lot for your help!!!

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