Originally Posted by
smarkinson
A Trek H2 fit for example with an effective top tube of 521mm is a size 50 and that has a headtube of only 130mm so you'd need to find another 70mm (nearly 3 inches) somewhere either in the steerer tube or up angled stem or both.
He's getting a custom frame built for a good reason. There's nothing off the shelf even close to those proportions. And not everyone is looking for a big saddle to bar drop even on the road.
The angles on the Trek 50cm are likely so far off that the fit wouldn't work out even if he could find a long enough seatpost and tall enough stem.