The Meaning of Life, the Universe, and Everything.
Do you have a favorite resource pack or style you like? I've always liked DokuCraft's medieval 32x and they do in fact have mod support for BuildCraft: https://dokucraft.co.uk/mod-support/buildcraft/ There are many resource packs out there that offer some form of mod support so a better way to go about this may be to look at the official website for your favorite pack and see if they offer what you're looking for. It's also worth noting that BuildCraft is also park of a few modpacks like Feed The Beast and Direwolf20 so if a pack offers support for those modpacks then there is a good chance it has assets for BuildCraft as part of their package. With a little more specifics about the style and resolution I may be able to hunt down something more specific, but hopefully this is enough to get you pointed in the right direction. Good luck.