I must have missed something.........why are the injectors coming out for a HG swap ?
and yes its a Buick design but Rover adapted it for their projects, there were once some very rare cast iron heads for the engine from the old Buick 215, straight swap over but with a greater flow rate than Rover ones
SD1 and 10 bolts then surpassed these from memory but for stroking these engines the old Pontiac (GM brand so Buick etc all part of it) used to be the way to go and would get you up to 5.5L with some work