Yeah, chainline is whats important. So its dependent on chain-ring position and bottom bracket length.
I use a Thorn crank-set and utilise the middle ring position and a 113mm bottom bracket.
This position will not work with all crank-sets and some bikes will need a longer/shorter bottom bracket.
The specification sheet for most brands of crankset will tell you what bottom bracket length for a set chainline.
From that info you should be able to tell how best to proceed (whether to get a longer/shorter BB or chainring spacers)
Usually the outer ring on a MTB triple crankset is very close to the correct 54mm chainline - or it was back when the standard chainline (measured at the middle ring) was 47.5mm instead of the 50mm current now.
FWIW, I ended up using a square taper double road crankset with a longer BB (110 instead of 103mm), a 3mm spacer behind the RH cup and with the 2mm Rohloff chainring spacers between the spider and ring. This gives a 54mm chainline with the absolute minimum Q possible on the frame I have, and used a set of cranks that weren't doing anything else.
Although you may be able to get the correct chainline (or close enough) using a more modern crankset, square taper cranks allow much easier customisation of chainline, and of the Q factor(s) on both LHS & RHS.