I have a 96 38 fever with 690 hours it runs beautifully how can I tell if anybody has updated the valve springs on these HP 500 ?

HP 500 carb? I guess previous owner gave you no proof of the work? There will be no way to be sure. Odds are they were done since the boat still runs. 300 hrs is the maint interval for valve springs and head gaskets and valve job strongly recommended. How long (hours run time and calendar) have you had it? I would start thinking about planning a top end refresh. If previous owner did them at 300 and 600 hrs, he would have mucho paperwork on the boat's maint history.

An HP500 with 600 hours on the original valvesprings is just waiting to ruin your pocket.
How to know if they've been changed? Well, the valve covers would definitely need to come off, but you CAN change springs without removing the heads.

At 600 hours, do a compression test and leakdown to see if you need to schedule a valve job. If they are still sealing good, then you can just toss in springs and umbrella seals.

If an HP500 has been run "aggressively" and it has 600 hours on it, then you need to rework the heads, new springs, check the retainers for notches, send the rockers to Crane for a refresh.
It's up to you on the bottom end (rings/hone) but a bad rocker will wreck your motor. Broken valvesprings are often not fatal. You just pick up a nasty backfire at midspeeds and above before they let completely loose.

If you have no documentation on heads being done, they need to be done now along with the lifters

I never recalled a HP 500 carb app the springs lasting 600 hrs . hell most we seen back in the day was 250 hrs to 450 hours a spring or more than one was broken. And when the springs broke came the water reversion.

3 years ago the last hp 500 I seen with 286 hours, A 2000 year model or maybe it was 2001 boat with 2000 year hp 500 's in it -- had multiple springs broken and reverted water.

I have nt seen a HP 500 carb since. I think they are getting rare especially bone stock ones.

They were probly done around 300. Which means they are on borrowed time second time around.

Much cheaper to do it now rather then run into a problem. Pay m now pay me later.....cheaper to pay now as it's running and not knocking ����