I'm looking at a 1999 353 Fastech that has the original HP500 carb motors. It supposedly has a little over 200 hours and I'm told it's had new exhaust manifolds and some head work. I'm planning on having a professional survey done on the boat and motors. Aside from the obvious stuff like water in oil, low cylinder compression and unusual running temps is there anything in particular that I should look out for on these motors? Thanks for any info.

Find out specifically what was done to the heads and if the valve springs were all replaced. That is the most important item. If they were changed, great. Find out when and with which springs. Even a survey will not tell you this. You should ask for receipts.

If the valve springs have not been done, they need to be done NOW. The factory original springs were notorious for breaking in the 175-250hr range.
Other than that, the engines are pretty much bulletproof.

Yes what Griff said! Keep in mind reciepts dont mean chit either! When I bought mine I had got reciepts from a VERY well respected builder in the offshore/race community and had broken/mismatching springs, 3 different valves, and the wrong cam in a 10K longblock

Thanks for the info. My surveyor wants to do a leakdown test cold and a cylnder deactivation test while running. This should paint a pretty good picture, although it may not tell us if there is a spring about to break. At this age I'm hoping they were done already. Thanks!