Not sure how good it is at copying modded blocks across Minecraft versions but you could at least use some sort of swapping wand to convert your big builds to vanilla blocks, make a template, go into your new world and get it placed where you want, with creative access you can autobuild it and then if you want a specific block texture you could swap it back out again. Not as simple as copy and paste but it could be a huge time saver once you get used to using it.