With a JAR CPL you will have completed all the requirements for the issue of a SA CPL, except the exams, and the flight test. To get a SA CPL off the back of your JAR CPL, you must complete all the exams, and do the flight test. You will need 200 hours TT, but there is no "flying course".
"To upgrade from a CPL validation to South African ATP, the requirements as per ANR’s 3.5(1) must be complied with."
ANR 3.5(1) lists the requirements for the ATPL, and it states that you must be the holder of a CPL. It doesn't state anything about holding a foreign CPL, so presumably it requires you to be a holder of a SA CPL.
Part 61, subpart 7 briefly describes ANR 3.5. without detailing the SA-CATS-FCL documents.
SUBPART 7
AIRLINE TRANSPORT PILOT LICENCE (AEROPLANE)
Requirements for airline transport pilot licence (aeroplane)
61.07.1
An applicant for the issuing of an airline transport pilot licence (aeroplane) shall -
(a) be not less than 21 years of age;
(b) hold a valid Class 1 medical certificate issued in terms of Part 67;
(c) hold a valid general radiotelephony operator’s certificate;
(d) hold a valid commercial pilot licence (aeroplane);
(e) have acquired the experience referred to in regulation 61.07.2;
(f) have successfully completed the training referred to in regulation 61.07.3;
(g) have passed the theoretical knowledge examination referred to in regulation 61.07.4;
(h) have undergone the skill test referred to in regulation 61.07.5;
(i) hold a valid night rating; and
(j) hold a valid instrument rating.
Experience
61.07.2
An applicant for the issuing of an airline transport pilot licence (aeroplane) shall have completed in aeroplanes not less than 1 500 hours of flight time, of which -
(a) 250 hours shall be as pilot-in-command or not less than 100 hours as pilot-in-command and 150 hours as co-pilot performing, under the supervision of the pilot-in-command, the duties and functions of a pilot-in-command;
(b) 200 hours shall be cross-country flight time, of which not less than 100 hours shall be as pilot-in-command or as co-pilot performing, under the supervision of the pilot-in-command, the duties and functions of a pilot-in-command;
(c) 75 hours shall be instrument time, of which not more than 30 hours may be instrument ground time;
(d) 100 hours shall be night flight time as pilot-in-command or as co-pilot; and
(e) not more than 100 hours may be acquired in a simulator.
Training
61.07.3
An applicant for the issuing of an airline transport pilot licence (aeroplane) shall have successfully completed the appropriate training as prescribed in Document SA-CATS-FCL.
Theoretical knowledge examination
61.07.4
An applicant for the issuing of an airline transport pilot licence (aeroplane) shall have passed the appropriate written examination as prescribed in Document SA-CATS-FCL.
Skill test
61.07.5
(1) An applicant for the issuing of an airline transport pilot licence (aeroplane) shall have demonstrated to a designated examiner, the ability to perform as pilot-in-command of an aeroplane the procedures and manoeuvres as prescribed in Document SA-CATS-FCL, with a degree of competency appropriate to the privileges granted to the holder of an airline transport pilot licence (aeroplane).
(2) The applicant shall undergo the skill test referred to in sub-regulation (1) within 60 months of passing the theoretical knowledge examination referred to in regulation 61.07.4 and within the 90 days immediately preceding the date of application.
(3) The skill test shall be conducted in a multi-engine aeroplane with variable pitch propellers or turbine engines, adjustable flaps and retractable undercarriage.