Looking to quiet things down a bit at idle speeds (I'm okay with noise at planing speeds) - twin BBC under cockpit deck floor are pretty loud. Can anyone make recommendation for engine room insulation that is legal and doesnt require huge bucks .... googling but damn stuff is priced like gold.

I used the Sounddown 3" insulation in my Sea Ray.
https://soundown.com/marine/
I bought the stuff directly from them. I think it was $700 for three 4x8 rolls of the stuff along with the 6" foil tape and the installation spikes.
I learned that any air gaps are the biggest culprit of noise, so if you have any gaps in your firewall, seal those with greatstuff foam.

This was the stuff I used.
https://soundown.com/products/acoust...me_3_1=&back=1
I would highly recommend it again.

Do not use any foam like that egg crate looking stuff. It dries out and gets sucked down your intake track of the engine Causes a lot of internal engine wear.

^ What phughes said ! ^
Got the Soundown stuff back in 2000 to insulate the fwd bulkhead and engine hatch , although in retrospect it might not have been really necessary but I had no baseline to compare with a before and after.
Also , if you don't mind a little extra weight with the lead sandwich foam that is certainly heavier than that egg carton crap that BUP is correctly referring to as disintegrating over time.
Our c0ckpit at all speeds is remarkably smooth and quiet. You can almost talk at normal voice levels past 3500rpm .

Thanks Guys! Swampy