What fan is ok to use for 73 400-4BBL w/ac?

[WH23G3G]

Ok I'm trying to get my 73 Charger 400-4BBL finally started up this weekend if I get these annoyances out of the way. All the trouble is because I had to get an aftermarket radiator. Mine was originally 26" but had a 28" bolted up to one side when I got the car. So I bought an aftermarket of 27 1/4" wide core. So I was able to make it bolt up and fit. But I had to use the original 73 28" fan shroud and it was hard to make fit on the radiator. So now the fan barely rubs it in one spot when I rotate the fan blade. I've got the massive 7 blade original 20" fan. I put a new fan clutch on but it's a thermal clutch. Can I use the replacement flex fan that measures 18" and has 6 blades without risking overheating? Everything's remained stock on this build. It also has factory a/c all new and a 3.91 gear ratio 8.75. So if I can fix this fan problem and figure out the fuel line to carb routing this week I should be able to start this thing up after 5 years of restoring. 

[FLG]

Just try it and watch the temp gauge. Its not like its going to rocket up there if its not working properly..heck you can start an engine up with no fan for a brief amount of time. I know my car takes about 15 min to actually get to the 140-160 degree range and i have electric fans, so there is no air coming through during that time.

[elacruze]

I've got the massive 7 blade original 20" fan.
Can I use the replacement flex fan that measures 18" and has 6 blades without risking overheating?

The factory used that massive fan for a reason.
you can certainly use the smaller fan, but certainly it carries some risk. I'd give it a shot, see what happens. Just be sure you have time to wait while it cools if it's insufficient.

[WH23G3G]

I was able to take the radiator out and cut two small rectangles out of the side of the original 28" shroud to make it work. On the aftermarket radiator it measures 27 1/4" wide core and on both sides of the core where the shroud rests they made two humps into it for some reason. So I cut two rectangle pieces out of the original 28" shroud and now it fits flush on the core. Instead of the speed nuts to hold the shroud to the radiator I used self tapping screws and since the holes on the shroud are elongated from the factory I had enough adjustment to fit the shroud perfectly. I installed the radiator and reused the original 20" fan and it doesn't rub anymore. My worry now is this original Mopar 20" fan going to flex enough to rub the shroud. Right now I can spin the shroud as fast I can by hand and it doesn't rub the shroud at all. I can't imagine this fan flexing enough. It's pretty stout and heavy. So it still looks original and hopefully it will work the same.