I believe that you are referring to the "manifold drain pipes"
You can see them as item 36 here:
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28851&SortOrder=35#top
They are originally long, small bore pipes attached to the bottom of the intake manifolds. Note that they extend to approximately the oil sump flange. The purpose of them was to "drain" excess fuel caused by flooded carburetors. Their very small bore & long length prevented them from inducing a major manifold air leak.
I personally consider them to be an unneeded extra since the carbs shouldn't be flooding in the first place & it is questionable how much fuel they could drain out anyway. I just soldered the fittings closed & left the pipes off. Moss lists them as not available. With millions of cars running around with no manifold drains, I don't personally think that it was a particularly good idea. I have never had an SU carb in good condition flood.
If you feel that the drain tubes are an advantage, or wish to be totally concours correct, you will need to find some very small bore tubing that can be full length. Note the small holding clips down near the oil pan flange. The long length & small bore reduces the effect of the air leak into the manifolds.
It appears that on your car, someone has used shorter pipes with a small drain hole drilled near the plugged end. While it will probably work, the problem is that the short pipes will drip fuel on the hot exhaust system. Not so good! Later engines used a short metal pipe with a plastic hose extension. The plastic tends to melt & is hard to route out of harms way. The tri carb engines did not have the drains. Take your choice.
D