Slight variation in temp is normal. Do you have an actual temp gauge with numbers or the factory C and H where we don't really know how cold C is or how hot H is?
If it is only rising slightly, and you are looking at a factory gauge, I don't know that you have an issue. Only way to tell is put an accurate gauge on it.
If it is indeed running TOO hot at idle only, then it is clearly an air flow issue. You said the fan blade was "a correct 5 bladed fan as far as I am aware". Check the diameter and make certain it is the correct one. There shouldn't be much of a gap between the outer edge of the blade and the inside edge of the shroud. My 68 El Camino has an average of about 1/2 inch gap. Fan blades should be approx 1/2 in and 1/2 out of the shroud.
You said you were on your second fan clutch. Are you sure it is correct? At idle, with the hood up, it should be pulling a lot of air at operating temp ("a lot" is only an estimate..... don't know how to tell you to gauge this, but if you have ever "felt" the air flow when one is working correctly, you know what I mean). Also (and this sounds really stupid, but I have ACTUALLY SEEN this one time on a car that came in the shop with a complaint of overheating at idle) check to make sure there isn't an obstruction of sorts on the radiator. The car we had come in had picked up a piece of cardboard about the size of a cereal box and it had lodged perfectly against the radiator and just sat there. Pulled it off and the car was fixed. Not likely, but don't overlook the easiest and cheapest fix.
In answer to your question, yes they made 7 blade fans. All the 69 performance models have a 7 blade fan. Not sure if it bolts to the 68 clutch. Someone here probably knows. 68 and 69 had different bolt patterns on the WP hub, as well as long pump in 69 and short pump in 68.
Highly unlikely you have any issue other than air flow given what you described.