Just measured my stock 32 bar. I measured the underside following the curve from where the bar meets the mounting to where the bar meets the opposite mount. 40-1/2 inches.
Here's what I did-----Took a crashed stock bar ---cut the ends off about 4 inches from flange mount. took my old stock bar & traced it on floor with soapstone to get the correct arch. heated 3/4 round stock steel to match the arch, then heat & bend remainder up to meet the flanges, then welded headlight mounts to bar, grinded all welds & had it chromed.--------Don