Chevy 454 through transum silencers/mufflers

[man-of-war]

I have a Wellcraft with a Chevy 454 high performance engine. The previous owner used it for racing and now I am looking to put some silencers or mufflers on the exhaust system. It is a through transum exhaust system. I looked at some other mufflers which were about 27" long and were recommended for that size engine. My exhaust pipes are 19" long from the elbow to the back of the transum. My exhaust pipes are 4" in diameter. I am looking to achieve a 35-50db reduction, if possible, and don't want to lose any hp. Thanks in advance for any suggestions you can offer me.