I bet you could drive home at lower speeds without the kit, and just the hardtop fastened at the front latch, I think some here have done it. [Edit: Disclaimer!! I haven't done this personally, proceed at your own risk
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The kit for the hardtop install is like this:
Porsche Boxster Hardtop Installation Kit - 986 / 987 (1997-08) - Pelican Parts Technical Article
Their parts page has the spin locks but it is hard to see if it includes the shoulder bolts as well.
101 Projects for Your Porsche Boxster: Project 69: Installing hardtop / fit kit Parts
You need:
QTY 1 - 986-563-713-03
QTY 1 - 986-563-714-03
QTY 2 - 999-219-041-00
There are also some kits on eBay from time to time that include a long handled wrench that supposedly makes it easier - I installed mine without using this tool so I don't know if it does or not.
https://www.ebay.com/itm/1997-2004-Porsche-Boxster-S-986-Hardtop-hard-top-Install-Kit-and-Perfect-Tool/190328535506?hash=item2c5076f9d2:g:ZT4AAMXQBlJSBdc s&vxp=mtr