It's not difficult to drill and tap holes in a flywheel to fit whatever pressure plate you want to run, I've done several. I've fit metric pp's to old flywheels and old pp's to newer flywheels. The pp's are supposed to be zero balanced so that's not an issue. Just take your time to locate and drill the new holes using the pressure plate as a template. I'm currently running an old pattern pp on a 5.0 flywheel with a T5. Just had to remove the locating dowels and counterbore the new bolt holes so they could accept the shoulder bolts that were used to locate the old pp's..
70 Maverick Grabber, 5.0 (Performer RPM 2.02/1.6 heads, RPM intake, Comp XE266HR roller cam, FiTech EFI, EDIS/MegaJolt ignition, long headers), T5Z w/Steeda TriAx shifter, 9" "N" case Trac Loc w/3.89:1, 31 spline axles.