Where are your valves when the pistons go to Top Dead Center?  You
know the sequence from *the book,* so where are the valves for each
cylinder when it is supposed to fire?

Check this with the valve covers off, engine off.  Turn the crankshaft
with some mother of a wrench.  Sounds like your timing relative to the
crankshaft is incorrect.

Lg

Try backing off the lash on the valvetrain.  Sounds like you did what I
did on my race car when adjusting lash - the valves are all hanging
open.  Or like Lawrence said, you gotta bad leak at the head gasket.

Are you sure you've got the plugs back on the right cylinders and coils
and in the right order?

Check for spark?  Check for fuel?
Maybe you've got something disconnected that's giving the computer a big
"negative" on the firing.

Dumb question, but WHY did you change the head gaskets in the first
place?  What was broken?

Ray

You do realize the intake and exhaust pushrods are different lengths?
                                    Bob