Sorry I didn't get back on line last night Nick. Here's a bit more info I found. The 3rd cross member is listed in the 1954 Chevy Master Parts Book under Group 7.012, GM# 593947. The book unfortunately doesn't give any dimensions.
The picture I posted above of the ebay ad cross member and still attached transmission mount (still available when I checked this morning) should be the correct unit for your needs. I know the price isn't too wallet friendly, but there aren't a lot being offered.
I did find another ebay ad for a
more used cross member at a much friendlier price, but it does not include the transmission mount.
A note on 46Sparky's measurement. Because the frame and mount are different widths at the front and rear of the piece, it might help if everyone measured both width point to use in comparing dimensions. The second cross member I included has pictures of it being measured at about 33-3/4" wide, but it appears the measurement is being taken at the forward (narrower) width of the piece. I'd suggest suggest measuring at both points on the frame (just ahead of and behind the 4 mounting holes) and compare.
I think you'll find yours to match the 1941-46 cross member.
Hope this provides more help than muddy waters.
