I installed a 283/TH350 in my 49 sub. I placed the engine about 3" lower and 2" forward in order to have clearance for the HEI distributor. I ground off the rivets and removed the crossmember, fabbed two brackets that lowered the crossmember 3"and then bolted it back in. I then bolted a pad to the crossmember to accomodate the rear transmission mount. Can't say about the LS1 Gen3. Pics in my photo album. Weeds
