Timing belt installation and timing 2004 3.0 v6

There are a large collection of repair manuals available online courtesy of a group that calls themselves Operation Charm. It includes the information you're looking for right here.

Timing Belt — 2004 Honda Accord V6-3.0L Service Manual - Operation CHARM

Hopefully that will give you all the information you need to finish your timing belt job.

While doing my homework to replace a burnt exhaust valve on my Volvo, I found that I needed a set of tools used to clamp the head back down and hold the camshafts in place. So I know there are tools made specifically to keep the camshafts from turning as you install a timing belt, although I didn't find anything being sold specifically for your car. Here's what looks to be the closest I could find that may work for you to hold the timing gears.

Amazon.com: CHRYMUM Engine Timing Tool, Camshaft Locking Tool, Engine Camshaft Alignment Timing Tool Kit, Camshaft Sprocket Clamp Kit, Car Main Cam Timing Sprocket Gear Locking Tool Set Suitable for Most Car : Automotive