I know this may sound stupid, so read if you dare.... Anyways, it is well known that the 8746 can only hadle 2 injectors. To handle 4, you need an external driver. I believe the reason you can't just simply splice into the injector harness is because you will cut the voltage to each injector. However, external drivers are still in the ealy stages for the most part.
So say you splice an extra injector in each of the two stock harnesses. This would cut the electrical current in half, right? So could you get away with doubling the pump shot via chip tuning to counter the loss of current? So for pure example, say you need 1 volt per injector. You splice your harness for 4 injectors and now only get .5 volts. However, you chip tune as to where you would have 2 volts going to each injector, even though in reality you only have 1 volt because of the spliced line.
I have no chip burning experiance, nor am I very educated in the physics behind electrical systems unfortuantly. So if this is completely off the wall idiosity, forgive me. Plus it is late

 

I'm not trying to say you don't know what you are talking about but .

Seriously, it won't work like you hope it would, but there is a way to hook up an auxilary driver board to power the two extra injectors needed for a fourbarrel tbi.

Check this tread out.Injector driver boards by yellow73bb

Steve

 

Yeah, I've been following that thread. Unfortuantly I wasn't able to get in on that order for the boards Hopefully, there will be some success with the drivers, and a second order will take place. I've got the holley 670 sitting on top of my 400+ hp (potential that is )383, and I'm willing to break new grounds and find what the power limit of a 2bbl tbi is. That's my "ground breaker of the year, now somebody else gets to try the driver boards On top of the fact I'm broke now, and still need the fuel pump and sfc's, I was just thinking of the most inexpensive route. Oh well.....the external driver boards don't seem to be too expensive to build.