theres no real rule of thumb on this,.
80 was first year for EST,
EST is what it was called til around 85 then ESC came out
ESC is a little more involved of a system than EST was,
both have pretty much all the same components and look to them,
the HEI 80-up were varied, some had vacuum and weights, some had one or the other only, and others had neither,
and yes the ones with the extra four wire weatherpack plug yep
ive seen all combos
the rule of thumb that says that if its got vacuum on it then its a non ECM controlled HEI is not true completely in some cases, GM was odd like this,
there are ECM HEI's with vacuum out there ive seen them i just throw them away though
swapping to non ECM HEI is nothing at all, no mods to be done, just swap and plug back in and ignore the four wire ECM plug, its cake walk,
id set engine to #1 firing postion TDC first though before removign the ECM HEI
then all you gotta do is swap on a non ECM carb too and then youre all done pretty much
non ECM carb be found on 80 and older and also on 80-up 8600 and up GVW trucks
80-up cars all models had ECM HEI thanks to their lower GVW
lower GVW always got the most emissions crap
in 80 i think some of the BIG 10 didnt get the EST system and could be liek that with 6200+ GVW
