Does the engine sound like it is pulling hard on the chassis dyno? My guess is that the ignition curve is wrong. You can make killer power on the engine dyno at WOT with a locked distributor but it won't necessarily work very well on a chassis dyno.

You can also kill a dyno run by starting at too low of a speed. Another thing to look at is the carb. Accel pump makes a difference when doing a chassis dyno pull but it doesn't necessarily matter on a WOT engine dyno.

There can be tons of stuff that changed between the engine dyno and the chassis dyno. A plugged muffler or a weak fuel pump in the car will kill a lot of power. I did a dyno pull once with my e-brake on. That killed a bunch of power!

Put on your detective hat and figure it out. The power is in there somewhere.