As whitsend mentioned there were 2 distinctly different 2.0 engines, one was the early 7 1-73 german built engine sometimes called the SOHC or "metric" and a limited production varient of the 1974 and later 2.3 lima engine used in the mid 90's ranger.
The original SOHC 2.0 was used in pintos 1971-1973, also produced in europe until the mid 90's and was used in seirras.. some were turbocharged and could deliver up to 300 hp. No other dsplacement variations were produced.
It can be easily identified by the camshaft mounting which has 3 bearings.
The late model ranger "2.0" was produced as a limited varient of the later 74- mid 90's 2.3 lima built at the ford lima plant. The limas were manufactured from 1974 to 2001 in displacents ranging from 1.3 to 2.5 liter and used in many ford products including pintos, mustang ii , thunderbirds,taurus and small trucks as well.as industrial engines.. None of the parts are interchangeabl e with the early SOHC 2.0 except radiator water and maybe oil. The late model 2.3 lima engines came in many varients including a 2.0 used in the ranger. This engine uses 4 camshaft bearings. The basic hp delivered by the 2.3 was 86.
Not sure about displacement but the 1971 engine was specified to have 9:1 compression and deliver 100 hp and the 72-73 specified 8.1:1 compression and hp reduced to 86.
73-73 pistons sit down in the hole about .080 i think..
Not sure if compression in 71 was due to pistons and if that would affect the displacemen.
To my knowledge all replacment / rebuild parts (pistons, etc) are now only available in the low compression version.
Some folks machine the blocks to increase the compression.