oil filled ones are perfect for modifying. Drill a hole in the bottom and drain all the oil. then cut a section out of the middle (above the spring cup) and remove the damper gubbings. then cut the spring cup off and weld it on further down. cut the threaded part of the damper off and rethread further down. Then insert the gubbins back in (make sure the valve part of the damper is at the bottom, away from the heat) and weld the top back on. refill with engine oil (thicker so more damping) and tap the drilled hole and tighten a bolt in with a seal. And there you have it, loweness but still have shock absorbers that work, springs that dont fall out of the cups and its not sat on the bump stops either.