Well, don't put a point on it yet - the BNC55AO (Goblin cone) is rounded - I'd call it "Elliptical" in RSim.

Anyway, it's 5" long and 1.325" diameter, which gives it an aspect ratio of 3.77:1

Not knowing the diameter of your tube, you could go with that ratio (3.77 x tube diameter) for the cone length (above the shoulder)

Now for the tube length. In the original or clone, the nose cone (as stated above) is 5" long. The body tube is 9". Which means the tube is 1.8 x the length of the cone.

If you bother trimming your cone (if necessary) to acheive a true upscale, you could trim your tube to 1.8x the length of your trimmed cone.

For the fins, well - you'd have to ratio the diameter of your tube against 1.325 to know the upscale factor for your fin templates.

Sandman is correct - it is pretty close to an upscaled 50x cone too. He *is* the expert, after all...