The best way to get use out of a hilift on an L400 or L300 would be to use the hilift mate.
Other than that, you'd have to fabricate or bolt on a jack point on the rear frame/front frame section.
http://www.hi-lift.com/accessories/lift-mate.html
Lift Capacity: 5000 lbs. (2273 kg)
David (delicat) has one and I'll be adding one to my gear box soon.
As for using a wooden base, I would not suggest it as wood can splinter/rot, etc... can't tell the load rating on a piece of wood.
There are spreader plates you can buy for a high-lift jack that spreads the load on the ground.
http://www.hi-lift.com/accessories/off-road-base.html
Or if you have sliders, you can use this adapter to keep the jack tooth from slipping off :
