I would think that putting it in together is faster, but I put them in seperatly and it went pretty quickly as well, I find that using the engine crane to lift the trans to the block once the engine is in is SUPER easy and takes like literally 5 min. to get it lifted in place and bolted to the block. So as my expierence goes it proabalby wouldnt matter, but if you can do it put them in together.