gimick or worthwhile? I hear conflicting arguments, and was wondering if anybody around here has any input on the topic.

has anybody tried machining their own? I cant see paying $60-$80 for a $5 block of aluminum, $3 in bolts, and half an hour in a machine shop. is there a good rule to follow when calculating the thickness of the spacer? has anybody experimented with a venturi style bore on a spacer?

97 TJ Sahara 4.0, K&N FIPK, 2.5" rancho, 31x10.5 BFG, black rims, tuffy stuff, hi-lift, AA SYE+tom woods CV rear, tera adj. upper rears, centerforce dual-friction, MSD coil/8.5mm, borla cat-back, warn steering skid, slotted rotors+high perf pads.