Something does not seem just right here. Could there have been a different problem such as what you are getting and the head gaskets were replaced hoping to correct what "they thought" was the problem?

 

No I told them it was head gasket they had white smoke coming out tailpipe and water in there oil

 

What happens if you set the initial timing to 0 BTDC or after TDC. Does it fire? If so, you may have a weak coil that is not capable of providing a hot enough spark to fire under the compressed cylinder atmosphere.

 

I think we all agree you have to have fuel and spark for it to run. If it starts with the timing moved around , but won't keep running or run smoothly and yet it ran OK before the heads were removed and reinstalled .
Could the EGR system be open preventing it from starting and/or running?
Are the vacuum hoses in the right place?
What about the PCV system, is everything all in the right place there ?
We appear to be shooting from the hip and don't know if all the parts were installed correctly or in the right places, do we?
We probably should start from the beginning and make sure we have everything in the right place. What do you guys think?

There are a few things by not being there we are taking for granted like how long was this thing apart, what kind of fuel quality do we have, did they change the oil and filter when the job was done?

 

Are all grounds verified connected? If the ground into the CPU that feeds the ground for the injectors is not there or doesn't have good contact, the injectors will not fire fuel into the intake. Thus, no start. See that a few times with poor grounding and "Green" grounds.

 

grahambo, since we haven't heard from you , is it safe to say you found the problem?