No Start

Three weeks ago, my son-in-law and I replaced the original 350 engine with a short block and had the heads re-conditioned at a machine shop. We have been unable to get the engine started except for very short periods of time, 3 seconds or so. The coil tested out of spec so it was replaced. The gasket under the throttle body was bad so it was replaced. The fuel regulator was changed. I checked the throttle position sensor with a digital voltmeter and compared it with a new sensor and the readings were nearly identical. A self contained timing light would only flash 5 to ten times during cranking and then no flash. I hooked up a 12v Sun timing light and it flashes every time. Hooking a spark plug wire to an old plug to test for fire shows a blue spark the first few times and changes to a red spark indicating to me a weak spark. The fuel injectors seem to be spraying too much gas and it is my opinion they are flooding the engine. I checked the engine codes and got a 12 only. I borrowed a good computer and installed it. No change in the spark color or starting. I un-hooked the fuel pump relay and cranked the engine. After four or five seconds, the fuel injectors start spraying. Today I checked and compared the engine temperature sensor to a new one and again it was nearly the same resistance. Tomorrow I plan to check cranking vacuum and compression. If things look good, one last thing I plan to change the injectors with a set from a 3.1 engine. This will be only a test to prove if the original injectors are spraying too much fuel. Any other ideas?