I'm not sure where you are located, but here in the province of Ontario in Canada with TSSA being the govonoring body would require a submission to be completed by a certified engineer to sign off on the equipment and the building structure to be able to withstand the extra weight. On the elevator side, he would search the shaft loads for the machine, the safeties, and buffers.The normal acceptable level is + or - 5% so if your car weight is 4000lbs an acceptable change would be 200lbs. You would have to weight the car before you did the cab work to know what the original weight was.
