Welcome aboard Aris ;-)
First three digits refer to engine type. There was 680 for 747cc, 839 for 782cc, 800 for 845cc and so on.
Suffix refers to engine ancillaries like carburettor, distributor, water pump etc in accordance with particular vehicle fitment. Either 800-01 or 800-05 types were originally fitted on the R4, other types as the -02 or -10 were fitted to R6 and R5.
-01 was the "basic" 845 engine with 28mm carburettor and 30HP (I think) power. -05 was fitted on other market cars (Germany, Sweden for example), had 32mm carburettor, water heated manifold and 4HP more power
Engines after model year 1978 had three digit suffixes /701 and /705 replacing -01 and-05 types. So I think your engine is named 800-701 rather than 800-07 (which is also the case with two '78 engines I have here).
In 1983 Renault changed again type prefix on the Billancourt 845cc, naming it B1B until end of production in 1985.