Just got my first slant six

Very good on the oil pressure!

Possible causes on the idle problems:
- A vacuum leak, leaning out the mixture; the choke enrichment when cold cold be covering that condition. Start by checking vacuum hoses for cracks or falling off, etc.
- The choke not coming off when the engine warms up and making the mixture overly rich. If overly rich, the plugs will have excess black carbon deposits on them. But it sounds like you eliminated that as an issue.
- Wrong ballast. Too much resistance will kill off a lot of the spark energy as the ballast warms and its resistance goes up. But that usually occurs within 1 minute. Just to be sure, what brand and PN of ballast did you get?
- Other voltage drops to the ignition system.
- Lesser probability IMO: Partial fuel pump failure or fuel filter being blocked.

Do you have a voltmeter? If not, it will be useful to get one for working on this vintage of car. You can check the charging system and battery health and voltage to portions of the ignition system, spark wire resistances, ballast resistance, wiring integrity, etc.