I have an 86 with a 4.3 and it regularly gets 21 - 23 miles per gallon combined (city/hwy). I can't answer for the 5.0
10ish
According to ElCaminoCentral.com 15 city and 22 hyway for the V6 3.8 engine.
Pretty much any 350 Chevy engine from 1968 to 1987 will work.
8* BTDC
The miles per gallon that an El Camino gets depends on the size of the engine. An El Camino with a Chevy 350 gets about 22 miles per gallon.
They are about the same in fuel mileage but the 6.0 is thirsty.
YES, It will fit right in it.
More then likely it is a 305
differen't trim and heavier duty suspension, also the SS had a bigger engine.
129 mph depending on the engine size
Depends on engine, transmission, gearing, etc...
12 mpg