Well, just in case anyone follows...... The Adventure Maps Parque Natural Sintra Cascais 1:25000 is accurate and there's an old Sunflower Guide that I got secondhand, which provided some ideas.
First day I caught a bus to Cabo do Roca, the westernmost tip of Europe and wandered north on the GR11, well waymarked, for about 8-9 miles, to Praia da Aguda, then cut inland to a bus stop at Colares, on paths with hazier waymarking.