OK, let me see if I have this right.
The carb that is on there now.....did not come on the 422707 replacement engine. Is that what you are telling us?
Where did the carb you are trying to use come from?
If it was me, I would build the carb and fuel pump that came with the 422707.
The fact that the replacement engine is now sitting in a chassis that could gravity feed has no bearing on the fact that a fuel pump is on the 422707.
I have seen these Opposed Twins in chassis's where the tank was either completely above the carb, or the fuel level was above carb when tank is full, but below carb towards the empty end of the trip. I have not seen an Opposed Twin Briggs that did not have an integral fuel pump/carb.

Ok I will rebuild the original carb and fuel pump.
This engine came from a neighbor that got it at a
yard sale and never used. The springs in the pump
were bad from corrosion,that is why I used the
other carb . I know that the carb that I have on
the engine now came from a opposed twin that
I scrapped ,should have written down the model
number . Both engines were free so all I have
invested now is my time .I want to get this
running so I can get my old White back from
my son-in-law.

I have it running with the replacement carb
I cleaned it again . I had drained the tank
3 times and strained the gas that I refilled
the tank with. This time I removed the tank and
found 2 pieces of a leaf in the bottom of the
tank. I do not know how any of this got past
the filter to the carb but it did . I am waiting
for the pump rebuild kit and will still put
the original carb back on. I prefer the original
as it has adjustable float,high & low speed jets.

Mownie 7 thanks for the help

Like mownie, I prefer to keep the original style carburetor with the engine. The original carburetor has a three screw fuel pump with a metal float. The carburetor is also equiped with an adjustable idle mixture screw.

During the last 4 years of production, the opposed twin carburetor was "upgraded" with a 4 screw fuel pump and other changes including the plastic float. These were most precise in metering fuel in order to meet emissions. These were non adjustable. If this is the carburetor you wish to rebuild, choose the repair kit based on the number of screws in the fuel pump. Earlier kits had most of the required parts, but amazingly, the needle valve was omitted. Later kits included the needle valve.

Both carburetors worked very well when properly cleaned and assembled. The carburetor with the 3 screw pump was more tolerant of the dirt that finds its way into the fuel system. The pump will not over pressurize the needle valve on these.

If anybody is installing a different engine into a tractor that has the tank under the rear floor/seat pan, and needs to hook up a vacuum operated fuel pump, here's a tip: In and near the top of the oil dip-stick tube, drill a hole to take a brass nipple, available at an auto parts store, or hardware store. Then run the vacuum hose to that nipple, and the problem is solved. And, no--it will not suck oil out of the engine!