I have a complete 1994 5.2 magnum with auto OD trans I would like to swap into my 1947 rat rod. I would like to use the oem efi to save costs etc. Any ideas?

I did it in my 1938 I was building. Was it easy? Nope.
Get yourself a 1994 truck manual WITH the wiring schematics. Your gonna need it. I used JUST the ECM harness and integrated it with an aftermarket fuse panel. It made life MUCH easier.
Also: solder and heat shrink every connection or splice. Do NOT use those crimp connectors. ECM's do not like loose or dirty connections, specially grounds.
On the 1994's, the O/D switch has to be a momentary ground, NOT an on/off switch.

Have fun!

Its a great swap, and its pretty easy and economical too. I finished the conversion this spring on my 68 fury and have been driving the wheels off it. The build is in the tech archives under E body magunum swap or something. There actually is a thread going on now 5.2/a518 am I crazy that people are bouncing ideas also. If you have a complete underhood harness from a donor vehicle, it makes it way easier. I wish I had done the swap a long time ago!