I cleaned the injector boss areas of my spare runners ready to weld in the injector bungs. The instructions don't mention welding but my bungs weren't a tight fit in the runners' counterbores so I wasn't happy going with silicon or anything like that. A couple of people have asked about the details of fitting these bungs so there's a few up close photos below which hopefully make it really obvious as there's nothing to it really.
Some kits come with O rings on the bungs to seal against the counterbore in the runner...some are a tight fit and the basic idea is to just press them in....some are slack and definitely need welding. I would classify the FIC ones as a decent sliding fit and would recommend they are welded into place. (In fact, I think I would always have these welded no matter what the fit was like but check the through bore for distortion after welding ).
The runners are filthy but they'll be blasted, degreased and powdercoated once these bungs are welded in...I only cleaned the welding area