L18 is a better bet for pollution and overall weight
A combo hard to beat is.....

L14 rods for perfect 1.751 rod/stroke ratio
89mm sleeved bores for 1941cc and the option
of running a Pro-swirl 3 valve Ka24E head.
ka24e pistons with 2mm shaved off for good deck clearance.

The sleeving is trivial most engine and repco places can do it.
L14 rods can be had from specialist datsun joints or ordered
from overseas.
A better option is to use local cheap and beefier e15et rods but need crankpins machined (175aud got quoted from repco) to 40mm meaning more power/less friction.



costs
Sleeved block for 89mm 350-400
Crankpins machined for e15et rods 175
Re-balancing crank and retreating crankpins 250
Ka24E pistons and head around $80 from Pick-a-part
(tear an e15et apart and put the rods in the sump for freebies)
L18 bottom end $60 from most wreckers.
Z20e timing front cover, chain and tensioner bits can be taken with L18 block.

KA24e turbo conversion on L20 block

When money allows you get one of the 2 inlet valves on the ka24e head (the one facing the sparkplug) resized to 35mm or 1mm over to decrease exhaust overlap and have a bias of increased flow towards the sparkplug area of the chamber.

This would be my engine choice for a datsun 1200 if I ever decide to own one. LPG would be the juice of choice.