[MaxD]

If you are buying a fixed back racing seat get one from a manufacture that meets FIA regs. That means Recaro, Sparco, OMP, Racetech to name a few.

You only need an "in" date seat if you are racing with an organization that requires it. NASA, for instance, will let you use an expired composite seat with a seat back brace and that brace doesn't even have to be mounted correctly, just present.

For your local interests in TT or DE, You just need to meet or exceed stock/OEM Seat/harness. If you upgrade, NASA is good with expired equipment as long as it is in good condition. PCA is getting much pickier. They now seem to think expired 6 point harnesses are less safe that 40 year old 3 point belts. Also if you use a multi point harness you must have a fixed back seat, roll bar and a HANS, actually good policy.

The rollbar on the Boxster is just fine to attach the shoulder harness to with 6 point belts (don't even bother with 5 point). You can use the stock lap belt mounting points, just get proper mounting hardware for the new belts. You need to drill two holes for the sub mounts. Get backing plates or big washer to reinforce the mounting points.

To echo again- Don't skimp on safety