\begingroup
\catcode`\^^^^ffff=11
\catcode`\@=11
\toks0{%
  local dimen_cmd = token.command_id'assign_dimen'
  local tex_params = {}
  local texmeta = getmetatable(tex)
  local texmetaoldindex = texmeta.__index
  local texmetaoldnewindex = texmeta.__newindex
  function texmeta.__index(t, k)
    local v = tex_params[k]
    if v then
      if v.command == dimen_cmd then
        return tex.dimen[v.index]
      end
    else
      return texmetaoldindex(t, k)
    end
  end
  function texmeta.__newindex(t, k, v)
    local p = tex_params[k]
    if p then
      if p.command == dimen_cmd then
        tex.dimen[p.index] = v
      end
    else
      return texmetaoldnewindex(t, k, v)
    end
  end
}
\def\InternalAlloc#1#2#3#4#5{%
  \csname new#3\endcsname#1%
  \global#1=#5\relax
  \etoksapp0{#2_params["\luaescapestring{#4}"] = token.create"\luaescapestring{\csstring#1}"}
}
\def\internalAlloc#1#2#3{%
  \expandafter\InternalAlloc\csname ^^^^fffe#3@#1\endcsname{#1}{#2}{#3}%
}
\def\texAlloc#1#2{%
  \expandafter\InternalAlloc\csname #2\endcsname{tex}{#1}{#2}%
}
\texAlloc{dimen}{pageheight}{11in}
\texAlloc{dimen}{pagewidth}{8.5in}
% \internalAlloc{tex}{dimen}{pagewidth}
\directlua{
  lua.prepared_code[\csstring#lua.prepared_code+1] = tex.toks[0]
  \the\toks0
}
\endgroup