Found something interesting for timing curve...for pre obd2.
 

Well,I was pondering around on the s10forum and found this post in a
"whats your ignition timing set at?"
this thread,post 18.
How much timing advance do YOU use, 4.3 TBI & CPI - S-10 Forum

il post the post here too :
The initial timing advance for my 1991 4.3L S10 Blazer is set at 0. I am using an AC Delco D1943C ICM with the 369 code stamp. Those modules are the ones that was first used on the 1985-1993 Chevrolet Caprice with the 9C1 RPO Police option. The 9C1 RPO General Motors part numbers were 16139369 and 10482827 which have been discontinued. Just because it is AC Delco D1943C, does not mean it is the 9C1 RPO police module.

The 9C1 RPO Police Option ignition control module provides 4 degrees additional timing advance starting at 4,000 RPM with a total of 6 degrees additional advance by 5,000 RPM. The AC Delco D1943A ignition control module MUST bear the 369 code stamp or it is not the police option module. Since the 2009 GM bankruptcy and after GM spun off their AC Delco parts division, it is unclear about the design, the quality and where AC Delco parts are made.
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So, Rockauto has this part # but problem is are they the 369 stamped code?

Google around,some interesting thngs on this is said on a few other forums.