I would be surprised if 0-6-0s and 0-8-0s caused problems on curves of about 3ft radius, it’s easy to provide sufficient sideplay on the centre axle(s). Problems are more likely to arise where there are bogies and /or pony trucks – see my post on this thread:
I’m having second thoughts about the wisdom of increasing the back-to-back and reducing the track gauge at the same time – I wonder if the wheels will be running on the radius between flange and tread. The EMGS manual includes a dimensioned sketch of the recommended tread profile which should allow you to work it all out. And here’s another link to a thread where “T-B-G” has actually built pointwork to EM-SF standards and run Gibson etc wheels with 16.5mm BTB successfully. The text below the photos of his track is very pertinent.
I know that someone used to sell gauges for EM-SF but I don’t think they are available any more – I cannot find any on the web. The link above has a dimensioned sketch of a suitable gauge which you should be able to turn up on your lathe.
Beginning to wonder if my new layout should be in EM-SF….