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.
More then likely it is a 305
YES, It will fit right in it.
differen't trim and heavier duty suspension, also the SS had a bigger engine.
129 mph depending on the engine size
Either a 200 or 231 cid V6, or a 267 or 305 V8
12 mpg