I installed a set of Hedman mid-length headers in my '68 300. I had to tighten them a couple times after a few heat cycles but haven't had any leaks since. Also, I had them powder coated which lasted all of 30 seconds before it flaked off from the heat. I would suggest high temp paint.
Hedman Hedders 78070 Hedman Street Headers | Summit Racing
I am running a mini-starter (which works great) and my block is from an RV and there was a small "ear" on the block that I had to grind down. Not sure if this is the same for all blocks but it was in the way and it didn't seem to be necessary. I attached a picture of this for reference. I was working on an engine stand for fitment to the block but I installed the headers after the engine was installed back in the car.
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