With the Powermaster starter, twice I've had to slightly clearance the nose housing to keep from hitting the flywheel. Not a big deal, just a few seconds with a die grinder took care of it. I've had pretty good luck with the Powermasters, until I went on Drag Week. When making 200-300 mile trips, it would get heat soaked during a fuel stop and didn't want to engage. I never had that problem on local shorter trips. I switched to the RobbMc mini-starter and never had an issue after that. It's a bit pricey, but a great starter. This on a '69 Mustang with Hooker headers.
I'll try to post a photo of the interference with the Powermaster....if Photobucket will allow me to.
As you can see, the interference is relatively minor, and easily fixed. That shot is before I added some clearance with the grinder.