Here is how I would modify the Rogers file to add altitude arcs. The first piece of code goes just before the first "showpage" opeator and add the arcs and nodus foot to the face.  The second piece of code goes just before the second "showpage" operator and adds the nodus line and bead to the gnomon.

I would just use Word Pad and copy/paste. I added comments to help you see what I did. Comments start with the % character.

Oddly, something in the original PS file prevents GhostScript from opening the second page, however when it is converted to a PDF, the second page opens ok in Acrobat Reader. Strange, but it is not my code, the original does the same thing.

Add this code just before the first showpage operator

%%% modification by Shadow Master to add altitude arcs and nodus foot %%%%%%%

/alt_ang [ 10 20 30 40 50 60 70 ] def     % define an array of altitude angles
/max_rad 150 def                        % def maximum radius, lowest alt angle
/alt_ang_lmt alt_ang length 1 sub def                  % define limit of array
/tang  { dup sin exch cos div } def                  % define tangent operator
/nodus_height max_rad alt_ang 0 get tang mul def         % define nodus height
/nodus_dist nodus_height latitude_deg tang div def     % define nodus distance
/first_hr_ang 18 Hmin sub 15 mul time_correction add def    % first hour angle
/last_hr_ang 18 Hmax sub 15 mul time_correction add def     %  last hour angle

.5 setlinewidth                                        % set line width narrow

% a for loop that takes each altitude angle, calculates radius, traces arc 
% from first hour angle to last hour angle 
0 1 alt_ang_lmt 
   {
   /indx exch def
   /alt_rad nodus_height alt_ang indx get tang div def
   0 nodus_dist alt_rad first_hr_ang last_hr_ang arcn stroke
   } for

0 nodus_dist 3 0 360 arc fill         % mark the foot of the nodus with a circle

%%%%%%%%%%%%%%%%%% end modification by SM for alt arcs  %%%%%%%%%%%%%%%%


Add this code just before the second showpage operator 

%%%%%% modification by Shadow Master to draw the nodus line and nodus bead  %%%%%%

0 nodus_dist moveto                             % go to nodus foot 
nodus_height 0 rlineto stroke                   % line to nodus and stroke line
nodus_height nodus_dist 3 0 360 arc fill        % make nodus bead

%%%%%% end modification by SM to draw the nodus line %%%%%%%%