🚀 go-pugleaf

I'm having trouble getting equally spaced aligned columns using
\halign in UNIX TeX 3.14t3. As soon as I use \multispan to write 
a title, the last column always ends up padded with more space.
The following examples show what I mean. Am I using \halign and
\multispan properly? Help greatly appreciated. (N.B. I'm actually
trying to solve substantially the same problem which arises when
I use the \use{n} and \Use{n} macros in Michael Wichura's TaBlE
from Personal TeX, a commercial product foisted upon me (!); any
any TaBlE wizards out there?).
                                     Thanks,
                                              Mark
------------------------------------------------------------------------
Mark McCaughrean    | University of Arizona | Phone: US + (602) 621 8347
Steward Observatory | Tucson, AZ 85721, USA | E-mail: mjm@as.arizona.edu
------------------------------------------------------------------------
 
\tabskip=0pt plus 1fil
\halign to\hsize{\hfil#\hfil&\hfil#\hfil&\hfil#\hfil&\hfil#\hfil\cr
0.00 & 0.78 & 1.83 & 1.48 \cr
0.00 & 0.12 & 0.73 & 0.46 \cr
0.00 & 0.10 & 0.67 & 0.40 \cr}
 
\halign to\hsize{\hfil#\hfil&\hfil#\hfil&\hfil#\hfil&\hfil#\hfil\cr
\multispan4\hfil This is the same titled using multispan \hfil\cr
0.00 & 0.78 & 1.83 & 1.48 \cr
0.00 & 0.12 & 0.73 & 0.46 \cr
0.00 & 0.10 & 0.67 & 0.40 \cr}
 
\halign to\hsize{\hfil#\hfil&\hfil#\hfil&\hfil#\hfil&\hfil#\hfil\cr
\multispan4\hfil This is the same table again but with an even longer
                 title just to make the point yet more obvious \hfil\cr
0.00 & 0.78 & 1.83 & 1.48 \cr
0.00 & 0.12 & 0.73 & 0.46 \cr
0.00 & 0.10 & 0.67 & 0.40 \cr}