frame widths

hi all, am building the frame for my 1928 model a tudor the plans i have call for it to be 35" at the rear cross member, seems narrow to me, the stock frame is about 42" wide at rear, the rearend i am using has spring mounts that i could use if i made new frame 42", anyone know of any reason the 42" frame will not work, would like to channel body also, this is my first attempt and i am trying to get this right, thanks for any info

depends what size tires you want to stuff under it.

If you channel it it shouldn't matter, the critical measurement on these Model As is the firewall. If I remember right they are about 28 inchs there.