s5 in s4 no start
 

ok guys so heres the deal i just swapped in a s5 NA engine into my 88 vert the s5 was just the block that was all. i kept the s4 LIM and UIM. i plugged off the hole in the center iron. the engine has good compression, spark, and fuel. ive checked and rechecked grounds and fuses as well as swapping in new plugs. still no start. it drove into the garage 2 days ago on the blown motor. ive reset the timing lord knows howmany times back to tdc and everywhere inbetween. what else could it be that causing it not to start. if i deflood it then try to crank i get one loud backfire then nothing after that.