If you can't find a large flange thrust bearing that gives the clearance you want don't worry. People ran the small thrust in Top Fuel for years.
I'm more concerned about longevity with the clutch pushing on the crank on a street car.
Will you be idling for hours with your foot on the clutch ?
If you can find the large thrust mains and they fit the block then use them . I've seen people say to file a very small angle (chamfer) on the rear side of the center main, in a 4 speed car, from the groove in the middle of the main bearing so it sends some pressurized oil to the rear thrust surface. I've done it to a couple engine I have in the works, and to a friends engine and didn't see any oil pressure issue because of it .
