The Steel Waterwitch drawings were produced by Dick Boelle, a Dutch boatbuilder. He seems to have got caught up in metricating the design as well as converting it for steel. This may explain why the lines and dimensions of frames etc are almost certainly incorrect. At least one boat built had a dire profile forward. Dick Boelle told me that he was expecting the first builder to loft the lines and record corrected dimensions - of course this never happened!
It is strongly recommended that these drawings are not used directly. Use the original table of offsets and even then check for errors.
Of course, once the lofting is completed and known to be fair, simple CAD files for frames, stem and other parts will allow the use of laser pofile cutting to produced near-finished items complete with all holes for attaching bulkheads etc. The laser profiling system wil calculated the most economical cutting plan to minimise waste. Some plywood suppliers can use similar methods for bulkheads and other parts.
All steel is supplied to metric dimensions these days: the steel specification to quote is BS EN ISO 10025 S275.
Note that the suggestion to use aluminium sections to stiffen the coachroof is likely to lead to severe galvanic corrosion if the aluminium is in contact with the steel. Full electrical separation would be essential.