using alternative fonts without changing texinfo.tex

[Neil W. Van Dyke]

Hi.  I've been trying to change the heading fonts used by TeX for
Texinfo documents to be smaller Helvetica-based ones.  I was able
to do this by modifying "texinfo.tex", but have good reason to want
to do it from the ".texi" files themselves.

I've been trying variations on this:

    \input texinfo
    @setfilename foo.info
    @tex
    \font\titlerm   = hvb at 20pt
    \font\titleit   = hvb at 20pt
    \font\titlesl   = hvb at 20pt
    \font\titlett   = hvb at 20pt
    \font\titlettsl = hvb at 20pt
    \font\titlesf   = hvb at 20pt
    \font\titlebf   = hvb at 20pt
    \font\titlesc   = hvb at 20pt
    \font\titlei    = cmmi12 scaled \magstep3
    \font\titlesy   = cmsy10 scaled \magstep4
    \def\titlefonts{%
    \let\tenrm=\titlerm
    \let\tenit=\titleit
    \let\tensl=\titlesl
    \let\tenbf=\titlebf
    \let\tenbf=\titlebf
    \let\tentt=\titlett
    \let\smallcaps=\titlesc
    \let\tensf=\titlesf
    \let\teni=\titlei
    \let\tensy=\titlesy
    \let\tenttsl=\titlettsl
    \resetmathfonts
    \setleading{25pt}}
    \def\titlefont#1{{\titlefonts\rm #1}}
    @end tex

    [...stuff ellided for example...]

    @center @titlefont{Your Title Here}

but that seems to have no effect on the title font used -- it still
appears in Computer Modern Roman.

Thanks,
Neil (nwv)