There are many ways to accomplish that. You can use string manipulation methods to deal with the possible formats you would expect for the header. See strfind, extractAfter, split, num2str, sscanf functions for example.
Here an example:
data.HeaderNumeric={};
for k=1:numel(data.textdata)
data.HeaderNumeric{k}=sscanf(extractAfter(data.textdata{k},':'),'%fx%f');
end
This adds all extracted numerics to a new field HeaderNumeric of your data struct. Note: This example is made for your above shown file. If the header includes lines with several numbers or numbers seperated by something other than x, this won't work and you have do come up with a more sophisticated approach for the format string.
