I think you misunderstood what was being said, maybe. Many of the S/C cars out there are excellent I hear, but a few certainly not, so it can become a bit of a lottery, depending on which way you turn.
Dreadnought conversions based on the KB supercharger are excellent, but no longer available. So a second hand car with one already fitted is the only option there.
A new/secondhand KB S/C, if you can find one, will need mapping properly. Major problem. Dreadnought are not allowed to map those they have not fitted, nor to provide the mapping to others. KB will not help there either.
Roush S/C ZT's were factory made (1 car only?), although some MGR factory engines escaped, with or without properly mapped ECUs.
One-off conversions, like #027 done by Chris Flanagan of Retro Sports, was MG Lifestyle, (using an Eaton?) for example, can be expensive.
Nobody knows how good/bad the mapping is on the Russian Paxton/Vortech blown car, #559, or how acceptable the conversion is, as far as I know. The car has recently gone "off radar" again, probably sold. Paxton no longer list a 'charger for the 4.6 2V.
... all in all, not an easy task any more, and probably problematical enough to make you think not worth while, hence the "Ferrari" quip above I imagine, apart of course from finding an existing converted car with known provenance?