I just recently insured my boat in CA -
size, hp, and top speed are now a bigger deal too. I have an 18' flatty, 750 HP, +100 mph. Had to fudge the numbers to 300 HP, and top speed of 60 mph - which is possible. Set rev limiter to 4500 rpm and retard the timing!
OT headers is tough. They just started clamping down on them. You can tell them you don't have them (unless they want a picture), but you run the risk of getting cancled if you have a claim for someone getting burned. Also, if you fudge on speed numbers and have a claim that includes higher speed than claimed, count on being cancled.
Progressive cancled a policy and refused to pay the claim on a guy with a Skater with twin 300's. He had a highspeed crash (over 100 mph) and tried to put a claim in. He had insured it as an 80 MPH top speed boat. Progressive might pursue an insurance fraud suit with the guy also.
The OT headers are tough because women get burned and then get plastic surgery and pain & suffering, along with a lawyer can hit 1 million easily.
I was upfront with my agent about everything. He recognized I was a resposible boater with many years experience, and he knew several people who knew me and vouched for my driving. I put through transom exhaust on for the pic's, but my agent told me not to tell him if I did any upgrades, like OT headers. But, if I did try to make a claim for burns due to OT headers, he would expect I would be cancled.