hi robert,
you can make the fitting out of solid then silver solder to the boiler. i would be inclined to fit a phos bronze bush into the boiler and screw the fitting into that. or you can have a look at keith wilson's DUKEDOG and BULLDOG design.
the main problem with the PANSY top feed is the check valves being covered up by the pannier tanks…a huge job to remove if the clacks play up. on mine i followed other examples of the prototype and fitted the clacks into bushes in the backhead with pipes going forward to the front of the barrel.
the top feed isnt the only problem with the boiler fittings… the backhead fittings and blowdown valves were all an after thought partly caused by LBSC's use of the SPEEDY boiler backhead and his row with ME at the time. the blowdown valve arrangement is atrocious as is the lack of a proper manifold/turret. on mine i fitted a proper manifold/turret of GWR type into a bush silver soldered onto the end of the firebox outer wrapper. due to the drawings showing too short a barrel, most builders cant do this, but you can always move the cab forward a bit or better still lengthen the barrel to the correct length. i fitted a 'vertical' blowdown valve on the backhead just above the foundation ring. LBSC's afterthought arrangement weakens the frames at their weakest point already.
cheers,
julian