Toyota Hiace Ride Height Adjustment 

It would be better to move the air intake housing to a different place alltogether.

A healthy 1kd will do between 9-10kms/L whilst a 1tr will do between 7-8kms/L

the lowering block/diff-spacer should be approx 2-3inches height,but it should vary as per your taste and not altering manufacturer standards.

I wouldnt recommend a shorter hanger to lower the van as this would affect leaf spring lateral movement. Height lowering is done by placing a spacer at the contact point between the axle and the leaf springs.

But they say to fit a lower block will cause axle wind up .