I think he means how to tell which series of Skyline an engine would have come from, identifying by the engine no. or another means.
If this is what you mean, personally I dont know Duh. But there must be guys out there that will tell you the date codes, whatever etc. for the various series of engines fitted to the 32, 33 & 34's. Physically, to look, at I think all the RB26's are almost identical apart from maybe the turbo's (different on the 34's) and possibly the engine breather pipework set-up.
We have an engine I would like to know of which model is it.The top cover is red like we have on the 34 but somebody might have changed them.
Is there any serial number to identify.
Other thing is an R32 and R33 front and rear diffs are perfect indentical as I can get a rear diff from a 32 and the front diff from this engine for the 34 as I want lower gearing