Different fuel pumps for 4.5 hp with integral fuel tank vs. auxiliary tank?

[Good Trout To You Sir]

Am considering purchase of an older 4.5 HP (Evinrude 1980 E5RC). Model in question has an integral tank. I am wondering how difficult it may be to retrofit with a barb to connect to an auxiliary tank so I may avoid a refill procedure on the water. OMC shows part numbers for 2 different fuel pumps. One for the model with an integral fuel tank, another for the model designed for use with an auxiliary fuel tank.
Thought the old square-style pump was uniformly used among the OMC small outboards of the era. Anyone know why the pumps for integral vs.auxiliary tanks would differ?
Were OMC models with integral tanks of that era always designed with fuel pumps versus gravity feed design?

 

[racerone]

You might find that the 4.5 block has a provision to mount the square pump for use with a 5 gallon tank.

 

[Good Trout To You Sir]

You might find that the 4.5 block has a provision to mount the square pump for use with a 5 gallon tank.

Though I have not yet seen it, I am told the 4.5 in question DOES include a fuel pump. Pumps fuel from the integral tank to carburetor bowl. For my purpose I would like to mount a fuel barb on the cowling and use an auxiliary marine tank, thus bypassing the integral tank altogether.
I am not a fan of a retro fit that supplies integral tank through an opening in the fuel tank cap. I much prefer to have an auxiliary tank connected to a fuel barb on cowling (that would feed directly to pump. Do you have ideas on mounting a barb on the cowling in a thoughtful way that might accomplish this goal?

 

[racerone]

You will find a spot on the side of the block to mount the little square pump I believe.-----Just take the time to look for it.

 

[racerone]

You will find on some of these motors that there is a wee rubber bladder ( red / orange ) colour that assists gravity in getting fuel into the carburetor.----You can not see this item !----You will find that the block has the provision for the wee square pump.-----That is used for about 40 years on many motors from the 1960's to the last years of carbureted engines.----Even used as a vapor extraction pump on the big 60 degree loopers.