I don't know if the '46 chassis/exhaust is close to the same clearances as a '35, but the pictures look similar. I went on the Walker Exhaust site, and chose P/N:17804 for my car. I had to use an ID to OD adapter for the inlet, but it fit perfectly and aligned well. Look at the Rock Auto site, and it will give you all the specs. Just a tip. The previous muffler rusted out from the inside, as it had no drain holes for condensation. I drilled a 1/8" hole just behind both end cap crimps, at the lowest point, to allow drainage.
https://www.rockauto.com/en/moreinfo.php?pk=130045