Surrogate Or Composite Primary Key?

My previous post was not really clear, so I'll try again with a (hopefully) better (even if longer) example...

Consider the following...

A JOB describes the processment of a document.
Each document can exist in two versions: English and French.
A JOB can have 1 or 2 TASK, each describing the processement of either the English or French version.
So we have the following:

A: JOB (JobNum [PK], DocReference, StartDate, EndDate, ...)
B: TASK (JobNum [PK] [FKa], Version [PK], Priority, ...)

that is there is an identifying 1:M (where maxium allowed for M is 2) relationship between JOB and TASK; TASK being identified by JobNum and Version (where the domain for Version is {E, F}).

Each TASK may require a TRANSLATION sub_task.
Each TASK may require a TYPING sub_task.
Each TASK may require a DISTRIBUTION sub_task.

For example, for a given doc, the English TASK requires TRANSLATION and DISTRIBUTION, while the French only DISTRIBUTION.

That is, there is a 1:1 not-required relationship between TASK and TRANSLATION, TYPING and DISTRIBUTION.
So we have the following:

A: JOB (JobNum [PK], DocReference, StartDate, EndDate, ...)
B: TASK (JobNum [PK] [FKa], Version [PK], Priority, ...)

C: TRANSLATION (JobNum [PK] [FKb], Version [PK] [FKb], DueDate, ...)
D: TYPING (JobNum [PK] [FKb], Version [PK] [FKb], DueDate, ...)
E: DISTRIBUTION (JobNum [PK] [FKb], Version [PK] [FKb], Copies, ...)

As you can see I am using the PK of TASK as FK and PK for each of the three SUB_TASKs.

To complicate things, each SUB_TASK has one or more assignments. The assignments for each SUB_TASK records different information from the others.
So we have...

A: JOB (JobNum [PK], DocReference, StartDate, EndDate, ...)
B: TASK (JobNum [PK] [FKa], Version [PK], Priority, ...)

C: TRANSLATION (JobNum [PK] [FKb], Version [PK] [FKb], DueDate, ...)
D: TYPING (JobNum [PK] [FKb], Version [PK] [FKb], DueDate, ...)
E: DISTRIBUTION (JobNum [PK] [FKb], Version [PK] [FKb], Copies, ...)

F: TRA_ASSIGN (JobNum [PK] [FKc], Version [PK] [FKc], Index [PK], Translator, ...)
G: TYP_ASSIGN (JobNum [PK] [FKd], Version [PK] [FKd], Index [PK], Typyst, ...)
H: REP_ASSIGN (JobNum [PK] [FKe], Version [PK] [FKe], Index [PK], Pages, ...)

that is there is an identifying 1:M relationship between each SUB_TASK and its ASSIGNMENTs, each ASSIGNMENT being identified by the SUB_TASK it belongs to and an Index.

I wish I could send a pic of the ER diagram...

Maybe there is another and better way to model this: if so, any suggestion?

Given this model, should I use for TRANSLATION, TYPING and DISTRIBUTION a surrogate key, instead of using the composite key, like for example:

C: TRANSLATION (TranslationID [PK], JobNum [FKb], Version [FKb], DueDate, ...)
D: TYPING (TypingID [PK], JobNum [FKb], Version [FKb], DueDate, ...)
E: DISTRIBUTION (DistributionID [PK], JobNum [FKb], Version [FKb], Copies, ...)

this will "improve" the ASSIGNMENTs tables:

F: TRA_ASSIGN (TranslationID [PK] [FKc], Index [PK], Translator, ...)
G: TYP_ASSIGN (TypingID [PK] [FKd], Index [PK], Typyst, ...)
H: REP_ASSIGN (DistributionID [PK] [FKe], Index [PK], Pages, ...)

I could even go further using a surrogate key even for TASK, which leads me to the following:

A: JOB (JobNum [PK], DocReference, StartDate, EndDate, ...)
B: TASK (TaskID [PK], JobNum [FKa], Version , Priority, ...)

C: TRANSLATION (TaskID [PK] [FKb], DueDate, ...)
D: TYPING (TaskID [PK] [FKb], DueDate, ...)
E: DISTRIBUTION (TaskID [PK] [FKb], Copies, ...)

F: TRA_ASSIGN (TaskID [PK] [FKc], Index [PK], Translator, ...)
G: TYP_ASSIGN (TaskID [PK] [FKd], Index [PK], Typyst, ...)
H: REP_ASSIGN (TaskID [PK] [FKe], Index [PK], Pages, ...)

I don't really like this second solution, but I'm still not sure about the first solution, the one with the surrogate key only in the SUB_TASks tables.