5 quick operation and Maintenance Qs

So, I have been driving my dart EVERY SINGLE DAY for the last 3 months. I have put 6k miles on her so far.

It's the 225 / . 1968. The motor is red, and the head is blue. Assuming the head was replaced sometime.

Lets just assume, since I have no idea - That Original owner did whatever he was supposed to do with the car right before he gave it to me and it hit 81k miles. I have it at 87k, and it's never had the Odo rolled over.

First: I'm assuming an oil change would be necessary, but I figured after giving it a new quart of oil every week, that all the original oil blew out the valve cover and plug tubes already. Maybe a full flush would be warranted though? Unfortunately for me no auto parts stores can find the seals for the tubes, and they are visibly blowing oil occasionally. Also no matter how many gaskets ive put on, the valve cover seems to gain too much pressure and blow oil out the sides. I've tried a variety of different breathers, all with the same result.

Second: How often should one adjust the valves on this motor? I have a feeler set, but would I need different tools for this car? I have only ever worked on newer OHC's.

Third: What else should be done in general? Or am I jumping the gun and need to wait longer for more maintenance? The car still has a miss at idle, which I can not find the cause for, and have installed electronic ign., Checked for vacuum leaks, etc. Still can't pinpoint. The car idles around 680 - 750 and when it gets to 1000, the miss stops, and the shaking subsides.

Fourth: I am still having trouble maintaining a heating issue. I have added a reservoir to the radiator to keep the car from puking on the ground, and somehow still lose coolant in very small amounts. The car runs fine around town, but if you keep to freeway speed (70ish) then the car heats up gradually over time till you let it idle down again. I can only be on the freeway for about 20 minutes at a time before the gauge tilts to hot. There's no steam or anything, but it's still a worry.

Fifth: There is a 5 bladed large fan on the motor, but no radiator shroud. I was thinking of making one out of fiberglass and carbon fiber and have the knowledge and parts to make it. My only question would be - is the fan supposed to sit outside the round opening of the shroud, inside it, or should it be halfway through it? I hope that question makes sense.