I think that's a fundamental flaw with your design. Without the original catamarans to support the saucer and Pylons, your model at that size is just gonna flop forward unless you have an extremely rigid metal frame in it.
This is especially true with the length of your pylons. I had that NX-01 kit, and the nacelles are fairly hefty for a kit. They sagged on the original layout unless you put a metal frame inside it. I just can't see this design being supported well enough to maintain its shape.