You might need to get a stepped high-tensile bolt machined by a local machine shop.
First of all drill and tap the flywheel hole to the next possible size up. Get a long high-tensile bolt and machine the other end to fit John's puller. Don't have a sudden 'step' in the bolt, have it machined down with a taper to avoid a sudden change in cross-sectional area. On the end through the puller make sure the threaded length is sufficient to retain it with good thread engagement using two nuts.
Best thing is to fit a pre-Verto flywheel/clutch when re-building.