360 10 1/2" flywheel

I have built a 360 to go in my 1971 Duster and will soon be ready to install but I think that I made a mistake. A couple years ago I found a 360 TRUCK flywheel and didn't stop to think, just knew it was a 360 flywheel. Well, I just got the 4speed, bellhousing and a 318/340 10 1/2" clutch and flywheel. I pulled the 360 flywheel down off the shelf, only to realize it was much bigger than the 10 1/2" flywheel. I am having trouble with the idea that a larger flywheel can fit in a small block truck's housing with the same bolt pattern as my bellhousing and still have proper clearance. Well, anyway, I guess that I am going to need a 10 1/2" flywheel to fit properly in my bell. I know that it MUST be a 360 flywheel with the drilled spots on the back side for balancing. Can I get the 318/340 flywheel machined to properly balance the 360? I would be a bit skeptical that the balance was right. Does anyone know about this or have a flywheel to fit? Thanks, Alan