Its the Pulsair system, my '85 classic had it originally. Basically each exhaust port has a tapping which draws in fresh air, effectively watering down the exhaust gases and reducing the emissions. IIRC it was for the american market originally and kept for the UK once they went EFI in the USA, gave an extra burble to the engine note!
Famous four used to make a blanking kit, was a set of 8 cap head plugs that just screwed into the head. Worth a phone call, failing that remove a bit of the pipe work and match the thread or cut and weld up the back of the unions.
