Hi PB. The cat can be done later without any problems whatsoever. Our cat is a direct fit replacement so there is no issues with doing it after the exhaust install. Our kit does fit the RL but IMHO the round tips don't suit the square openings. We have done a few RL's at our store and we reused the stock tips. We have tried a lot of different tips and some are acceptable but we haven't found any that match the car as well as the originals. It would be possible to sell the kit without any tips, then you could get a shop to weld your's on. Another possibility would be to cut off and ship us your tips and then we could use them for your kit... Hope this helps and thanks for your interest.