Any competent machine shop should be able to handle it , the seats & rails are available , drill the holes & either weld in the seats or epoxy them in & drill the rails to match the spacing , Holley had rails available when I bought them .
With EFI the intake is less critical , wet intakes [ using carbs ] are more finicky as the fuel needs to stay suspended in the air flow , with EFI the intake is dry so as long as it flows air well it will work . Edelbrock makes the 440 Victor predrilled with rails to match , check with eddy on the 400 application , I have not heard of one but they may have it available .
The injector size is basically determined by HP , I used a 75 lb/ hr injector but we dynoed the engine at 702 gross Hp & 630 ft lbs , I used 2 Walbro inline fuel pumps with a 3/8" fuel line to each fuel rail & a single 3/8" return line through a single Bosch pressure reg . Depending on the power you may be able to get away with 50 lb / hr injectors . I anticipated we might make close to 800 hp & wanted to make sure the engine would not starve & go lean so we shot high & actually had less margin than I thought .
