I had an 83 242T flathood for 11 years. It had the smaller flywheel. It is about 7 lbs lighter, which is better for high performance use. It will also hold all the power your motor might make, if equipped with the right clutch. I used a CF II, which may no longer be available for the Volvo. I have read of two reliable reports over the years of CF I not holding at high boost levels on modified Volvos. I would not buy a CF I if you have high power ambitions. My CF II held 18 psi max boost in daily driving for the last couple of years that I had the car and 14-16 psi max boost in daily driving the rest of the time, including several years with occasional nitrous use (60-80 hp worth) that broke an M46.
I would buy whichever car is in better condition. Flywheels, hoods, grilles, etc. can be changed. Getting a really good 242T is the harder part. The myth about flathoods having special engines is a myth. I would not expect the flathood to be a valuable collector's car one day. Get the best 242T you can find, do a "performance daily driver" restoration, and enjoy it. They are great cars.