I’m trying to figure out why you have a spring clutch. Is this a 66? I’ve always understood the 10" spring clutch to be a 3.8 thing.
IME the spring clutch is quite noticeably stiffer than the diaphragm. The diaphragms I’ve driven felt downright modern whereas my spring clutch is a major workout. Of course there are other variables like whether the pedal return spring is in one piece or broken, and how tight the slave spring is adjusted.
Judging from the photo of your flywheel it appears to me to already have two sets of drillings, for both type clutches and inner course and an outer? Whether it’s an original that has been modified or is a replacement type I couldn’t guess. I know places have been selling dual purpose flywheels for a while.
The one and only benefit I know of with the spring clutch is that it is stronger. It won’t slip under load until the friction plate is basically gone, so it’s good for high performance racing engines. I’m doubting a 2+2 falls under that category.