I put a 350/TH400 in a 47/48 frame. I did not touch that crossmember. I also used the bolted-on original transmission crossmember for the TH400 by unbolting and sliding it back until it was centered under the transmission tailshaft mount. I did not have to cut it either. When I mounted the cab, I had to slightly massage the lip of the forward edge of the transmission hole.
After reading about all of the "aftermarket cross member this" and "cut out that", I was surprised how easily my method of installation worked.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission