Intake manifold length for mor torq

[kiwicar]

if you go for lPG only you can use a much higher compression, 11.5 to 13:1, in that case it is worth looking out for a flat top piston set which will help torque off idle allot. Yes the 4.2 crank is longer stroke so will give more torque. Can't tell you more about the LPG side or the cam without timing figures. a longer inlet system should give more torque if designed right, as will a ram pipe into the plenum chamber.
Mike