Individual runner manifolds have much different cfm demands then a single plenum intake does.
Throw away that Holley cfm chart for IR's.
The 48's were really developed for Shelby's 289 Cobras.
They start to show restriction issues at around 5,500 rpm's on a 289. That's with 42mm chokes too.
58mm IDA's were actually developed specifically for 427 comp Cobras. Not many were made. Some say only four complete serial numbered sets.
The 351c under comp demands needs something like a 54 of 55 mm throttle. Actually the number is probably the size of the intake valve seat opening or there abouts?
54.6mm, plus or minus, is the maximum the 48 IDA manifold ports can be bored out to and realistically the Hall manifold is the only one available.
That manifold has about that limitation of porting as well.
There are two other IDA manifolds that were made for the 351c that I know of. The Holman-Moody, and the Detomaso lettered one.
Hall was the only individual I know of that had a DT manifold. Years ago I wrote to DT inquiring and I still have the letter somewhere but the entire setup from them was about $865, circa 1980. Coulda', wouda', shouda'.
I have never had either in my hands but was told that the HM was the first to be made, the DT is a copy of it, and the Hall is a reinforced version of the DT.
So in a nutshell, the 32's are too small and therefore have little attraction to someone who is looking for a max effort performance induction system.
Of course this is all from my perspective which admittedly I am quite a bent individual to begin with, so you need to keep that in mind and take what I say with a grain of salt?