Clearance is tight with the long WP w/clutch fan - any recommendations?
I have a 5 core copper/brass that is 3.5" thick and yes, clearance is tight. There is a tad less than 1/2" between the clutch and core which means I have to remove the fan to swap a belt if need be.
So, I think with a 2.5" or 3" core, you will be fine with near an inch clearance.
Also, due to the design of alum core's much larger tubes, the 3" would be about the same capacity as my 3.5".
That is why people think alum cools better than copper. It doesn't. Heat exchange is almost identical between the two materials.
it's because alum cores are more compact for the same given capacity, so a thinner alum core appears
to cool as good as a thicker copper/brass..
More capacity is always better so I'd go the 3". I doubt it will be an issue in traffic when the fan has to pull air through it either. My 7 blade clutch pulls air through my core just fine and the temp has always been 5-10°F above the 180° thermostat. (454, 12:1 & 522 rwhp)