Stewart Wilkins knows his datto stuff, thats where i get my bits from...also try SSS automotive although i think they may have moved away from the older stuff now....
The recipe for a good torquey L series combo consists of(ive built one b4)......
L18 Block
Double counterweight crankshaft, I avoid using the single weight cranks.
L24 flywheel, lighter than the 4cyl ones and accepts the larger diameter clutch plate and pressure plate(i think Navara is lighter again, but dont quote me)
720 4WD Clutch
L16 conrods, as they are 2.9mm longer than the L18 rods. This improves the rod ratio from 1.66 to 1.7, giving more bottom end torque. The standard datsun piston has a 2.9mm deep dish in the top. So by fitting L16 conrods and machining the piston flat, you end up with a zero deck height, flat top piston bottom end, that has a better rod ratio than the L20B (1.68).
60 thou oversize pistons
Stanza SSS gbox...better ratios and reverse is directly above 1st making it ideal for a kana car. R 2 4 1 3 5
You can take an L18 to 140thou over and use toyota pistons if u wish...they have massively thick bores.