s14 block and ecu work with s13 head?

[vervedatsun]

Ok guys,
im about to junk the whole deal...
bought the car ka24de from a friend, and it wasnt running, but i do remember riding in it etc... when he owned it, so i know the motor is good.

so here it goes he blew the head gasket and pulled the head broke some cam bolts of in the head tried to use an easy out kit broke those off on top of the broken bolts.
i know...
he went to buy a used head, found one. he had it gone through bolted it on and then went to put the cam cover on and uh... it didnt fit turns out he has a s14 block and all components and a s13 head now.
i took over and got the upper timing chain cover and valve cover from people on here.
Heres the thing there is something going on whenever the motor hits 4500 rpm or so it falls flat on its face..hard.
it had vaccum leaks out the ass, i had shogun style go through it and they said it isnt a vacuum leak.
He said that at higher rpm the two different heads are a little different on timing/fuel etc...
the s13 needs the s13 engine harness and ecu same with the s14.
Weird thing is the motor will rev till the moon if you slowly put your foot into it, but if you drive normal or push quick for a rev it basically almost dies then as soon as you let off its fine idles and everything.
Cam tooth off or fuel pressure or what or is he right about the wrong ecu
Just wanted some other opinions before i go through all the work of changing that and spending the dough.
Running out of options though