[jakeru]

Others can chime in, but it sounds like if the only thing powered about your seats is the back recline, you may already have the lightest ones. Certainly sounds lighter weight than my 2001's 8-way powered seats!

I'm not sure if completely non-powered Boxster seats exist, but maybe others can chime in.

The "sport" seat option, if you can find some to alter the spec of your Boxster to, might be nice for upper body support. Not sure if they would be as light as what you have, though.

I'd do a 5- or 6-point harness (I think that's still SCCA street class legal, yes?) for additional body restraint and support with the lightweight seats you seem to already have, before spending the $ on finding some (generally pretty sought-after, so probably not cheap) sports seats, though.

For other stock class legal weight savings, look into some custom, aftermarket wheels (might not be cheap, but you're talking unsprung, rotating weight, so it's important! Plan to spend some $ here!), and a "tiny" battery. Muffler is, of course, another area to look for legal weight savings.

I think on the replacement wheels, you can legally add as much as .25" wider offset, and use whatever dimensional specification is "best", (widest 17" option, maybe - not sure if 18" is available any wider, probably heavier if so) which is available for your 2001 model car. But check the rule book, (my knowledge is a few years dated.)