Here is an illustration of our smallest standard Stanforth Conway size with an effective seat tube of 52.5cm and actual sea tube length of 43.1cm. We have estimated the saddle height at 617mm based on a height of 5' 1". A custom Conway for your specific measurements might be a better alternative to this size as assuming an inside leg measurement of 699mm (27.5") - the standover height of the bike will be circa 3cm higher than your inside leg, at 729mm, so it might be worth considering bespoke geometry of this frame - we would recommend a sloping top tube tailored to your inside leg, a greater bottom bracket drop and potentially a shorter top tube. Please email us on firstname.lastname@example.org to discuss your custom Conway.
To measure your inside leg: 1. Get a book and stand with your back against the wall, 2. Place the book in between your legs as high as it will go, 3. Move away from the wall keeping the book against the wall and finally, 4. measure from the top of the book to the floor. It will also be useful to measure the saddle height (bottom bracket centre to the top of the saddle) on your current bike and compare it against the illustrations.
We look forward to designing a bespoke Stanforth Conway for you.