I did a 400m to 351W Swap.. it has GT40p heads. so headers for it are hard to get used and there a tight fit.
as for the drive shafts. the rear drive shaft fit in like before no issue.
front drive shaft fits perfect also. but the issue here is [ 79 broncos didnt come out with 351W until 80s. so your gonna have a issue with your Shift linkage rubbing your Front drive shaft.|

if its a C6 SBF bellhousing then its the same shaft as your old 351m BB bellhousing trans