GT40P head swap problems....

I have recently done a GT40P head swap motor for my 69' mustang, and I can't get it to start. The heads have the stock springs and rockers, I had to get longer pushrods for the Hyd. flat tappets (5/16,6.9"" TFS) My cam specs are as follows: SAE DUR. ******** Cam Lift
Int. 300 Exh. 306*********Int. 311 Exh 325
.050 DUR.
Int. 224 Exh. 234
The guy that built and assembled my shortblock said he degreed the cam 1 Deg. Advanced. I have spark, I have tried the 351w firing order, I have tried 10Adv-10Ret timing on my crank/ignition timing. It seems to get closest at 3deg. advanced on crank, but it sounds like it is being choked or something. It starts to fire a little when the sarter is ingaged but as soon as I stop turning it over it quites. I also have fuel getting to the cylinders. The only thing I can think of is maybe the valves aren't opening enough? Any insight would be great thank you.

I turned my engine over to NO.1 TDC, then just put my distributor in and set the plugs accordingly......

Well, I got my induction timing light out and it turns out i just needed to retard the distributor. I knew i had the NO.1 on the compression stroke because i was checking it with a feeler. I just didn't think my distributor needed to be turned so far to the left. Its a brand new motor and the first time i started it, it has been a 3 month build and I coudn't be happier right now. Thanks for the posts, now on to the T56 & 8.8 swap.