Making changes to an RPG program

Hi everyone
Before I forget - we are on V7r3

I have been given the task to make changes to an RPG program - that was last changed in November 2011

Whenever I need to make a change to an RPG program, my first step is to convert the RPG source to RPGLE source by using the command CVTRPGSRC

Having said that, its been many moons since I last converted an RPG to RPGLE
Until now

The reason I have created this e-mail, is that I have decided to try and take it one step further (be careful what you wish for) and see what it would take to convert to free
Its laborious
We are having RDi installed, and I am one of the lucky early ones - so its been fun learning about RDi as well

Here is my question

Calling external programs

The code I have is
SWAP C CALL 'SWAP'
SWAP C DUEDAT PARM DUEDAT SWAPDT

Its been a while since I saw this type of code, but I believe the translation is
Call program SWAP using the parameter SWAPDT, but populating SWAPDT from the field DUEDAT and inserting the answer back into DUEDAT when returning from the called program SWAP

The field SWAPDT is defined as
dcl-s Swapdt packed(8:0) inz(0);
The field DUEDAT is defined
dcl-ds Duedtds;
Duedat zoned(6:0);
Oiduem zoned(2:0) Pos(1);
Oidued zoned(2:0) Pos(3);
Oiduey zoned(2:0) Pos(5);
end-ds;

How would the call translate into free?
Hope this makes sense
As always - all responses gratefully accepted
Alan Shore
E-mail : ASHORE@xxxxxxxx<mailto:ASHORE@xxxxxxxx>
Phone [O] : (631) 200-5019
Phone [C] : (631) 880-8640
'If you're going through hell, keep going.'
Winston Churchill