Pitman Arm Compatibility

Ok, so I've got a bit of a Frankenstein Duster. Brief History - Originally had a 74 slant 6 car. It was too rusty and eventually had to pull it off the road for safety reasons. Found a 73 shell in great shape but had been turned into a drag car, and eventually gutted. When I bought the shell it was really just that, a shell. From what I can tell, the car was originally a 318, they had put a 440 in it during the race era and pulled it. For cost reasons, I took everything from original 6 cyl. car and put it into this car (including k frame). That was several years ago.

Now, I am in the midst of replacing my steering/suspension system. I need to replace my pitman arm, but the part that is currently in the car is not the same part that I'm being prompted to. Ex.when looking for which one is the right part, you are asked what engine you have and whether you have manual or power steering. Since I currently have a 225 and manual steering, but originally had 318 with steering type unknown, also throw in the 440 factor and what they might have put in at that point, I'm not sure which part I should get to make it work properly. I have a V8 k frame and hope to in the near future put a V8 in, but don't want to make assumptions at this point. I need the car to ride and drive well with what I have for now. So if anyone has any input to help me with this, that would be much appreciated.