Looks like the mould tools have got worn over time, allowing too much plastic flow into the tail plane tabs. just file down the tabs, or slightly enlarge the slots, and they'll fit. I seem to remember that, for whatever reason, the nose intake is moulded 'solid' internally, and is quite thick too, making it a b*gg*r of a job to hollow out.
I think I made a 'FOD' guard for the one I built 30+ years ago. I have one spare from one of my Academy kits if you want it H ?