Thanks for all the inputs and suggestions from everybody. It's good to learn from other's experience.
So I got the 50 Liter drum. Looks a lot more portable!
I marked off the holes and opened them up to accept the brass fittings. Surface ground clean in preparation for silver solder.
25mm Brass fitting:
Fitting is a nice snug fit in the hole:
Engine running with cooling!!
I dug in my "box of pipes" and found perfectly suitable radiator hoses I replaced years ago on a VW I had.
The Lister water valve was a solid piece of rust. It took some heat and 4 lbs hammer to get it apart. After cleaning I lapped the valve with some valve lapping paste.
The drum and valve was trial assembled onto the engine to see how (and if) it works. After sorting the engine framework, the valve and the tank will go green.
I'm toying with the idea to mount the alternator underneath the cooling tank to reduce the footprint of the genset. Mounting it this close to the engine will slightly reduce the contact area the belt will have on the alternator pulley, but will it be significant enough to worry about?