If you are going to pull the engine for this work, have someone check valve-stem-to-guide clearance to ensure new unworn valves fit properly. With all OEM iron heads, the valve guides are part of the casting. To use replacement guides, the originals must first be drilled out, the holes reamed to size and new replacements pressed in, then reamed again to valve stem size. Or you can have good guide bushings installed and avoid the drilling step. All this at about $100/hr costs $$$$, which is why it's often cost-effective to buy new aluminum heads that already have the guide work done, a competition valve job and thick, flat, uncut deck surfaces. They will be configured to Boss-351 specs.
Plus you lose around 30 lbs from each head, which makes later working on an installed engine far easier, and you gain better airflow & more power from repositioned intake & exhaust ports. But if you do this, stock headers will not bolt on without rework. If the wt savings interests you, another 40 lbs can go away with a matching aluminum intake & aluminum waterpump & pulley, to total over 100 lbs gone from your engine. That's like NOT always having a passenger riding with you, in terms of fuel mileage and performance gains.
Note that nearly every advantage above becomes iffy when cheaper chinese castings and/or valves are involved. Also note that ''CHI'' brand aluminum heads are made in Australia and are fine to use. If you paint aluminum heads Ford-blue, all but the most anal onlookers will think it's 'stock', if that matters to you. One early racer (who shall remain nameless) once used a coat or two of iron-based paint, then Ford blue on top so a magnet would stick to his alloy heads during inspections. If your locale still has smog checks, this could help.