Yes, I found myself facing the same issue. I think the easiest way is to deal with % yield instead. You can get % yield from pts/lb/gal by dividing by the reference which is sucrose at 46. For example, pale malt 2-row US has pt/lb/gal yield of 36. % yield = 36/46 = 78.3%.
You can then determine the pt/kg/l by multiplying this by the reference for sucrose in metric units which is 386 pts/kg/l. For example, the pt/kg/l yield for pale malt 2-row US is 0.783*386 pts/kg/l = 302 pts/kg/l.
Alternatively, you can do this all in one step: 36/46*386 = 36*8.3913. Just remember the conversion factor of 8.3913!