The issues I can see are the 409 has no pulleys, flex plate, motor mounts, brackets for alternator or PS, distributor or dip stick. What if any of the components can be shared from the 327?
The previous owner purchased a Edlebrock Perfomer intake and chrome valve covers there is a yellow plug in the intake just ahead of the distributor hole can that be used for a pcv? The valve covers have no provision for pcv either and I don't believe I've ever seen a 409 with a pcv or will I need to find some kind of crankcase vent tube?
You can reuse the 327 pulleys though there is a strong possibility that the pulleys or brackets will have to be shimmed with either shims or flat washers to get them to ALL
Motor mounts will bolt up so they can be reused but they will break as you need the type that were interlocking. They are sold mail order or you can go to a polyurethane motor mount that is interlocking.
Distributor is the same. The only difference is in the weights and springs used on the advance platform to match the torque curve of the big block. You can have the distributor recurved professionally on a Sunnen distributor machine or do it your self with a kit and guess at the curve by trial and error.
Dip stick can be replaced with an aftermarket one. Lokar sells billet aluminum knob dip sticks; but Moroso, Milidon, and Steff's, and other oil pan makers all sell dip sticks that can be cut to length.
Brackets are going to be a problem as they are specific to the engine.
The plug is filling a vacuum access port used for power brakes, engine vacuum gauges or for PCV. The 348/409 was built originally for a road draft tube so access to the vacuum is through the back of the block. You would use the same PCV system as was on your car now just transfer everything over. PCV systems first appeared in 1962.