The mechanical pump is located on the lower right side towards the front of the 454 engine. Best access is from the wheel well or laying in front of the wheel and crawling underneath.
You will likely also have an electric pump about midway back to the fuel tank. This is a booster pump to help overcome vapor lock problems.
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)