Ok so I spent a few hours tonight searching for the correct ECM pinout comparisons for any one doing a swap of this nature. Here is the Link for the 5.7l 97-03 Vortec VCM Pinout http://www.lt1swap.com/1999_vortec_5...r_end_view.htm

Here is the Pinout for the 2000 Blazer 4.3l https://blazerforum.com/forum/2nd-generation-s-series-1995-2005-tech-41/need-wiring-help-33689/
Special Thanks to swartlkk for the blazer pinouts.

So Basically they are the same except for The PRNDL Indicator, the 4th O2 sensor Addition, the tach output, and the injector controls need to be moved around. All the color codes are the same between the two injector plugs. (Aside from the 2 New that need to be added.) May have mmissed some things. But maybe this will save you some time.
Anyway hope this helps someone. It Definately helped me.