Since your car is set up for an FE, if I were in your position, I would stay FE. Price a set of headers that would bolt to a 385 series and your side pipes. Then the mounts and flywheel, bell housing, etc. Too much of a head ache, let alone the cost.
The 427 center oiler, if it is what it is advertised to be, is worth the money if that is what you want. It is priced at the top of what it is worth from my perspective, but if you needed it to restore a car it is a steel. I wouldn't use the heads. With the crank and rods it would be tempting to build it and use them. So you would have another $2500ish in good heads. By the time you get a cam and valve train maybe another $1500. So you could have it done right for about $12K. Obviously you want some work done on the
oil system.
Toss a stroker rotating assembly in it and you will add $1500-2000 and make a bunch more power.
I would have to look things up but I think you can have a 390 block stroked to 445ish built by any of the builders that visit this site for the same money, and it would likely make more power than a 427. Then the builder would stand behind it.
PS
Craft budget at 500 HP $10995
390 FE 416-445 Budget Blueprint Crate Engine - Craft Performance Engines
Craft street at 525 HP $13895
390 FE 416-445 Street Crate - Craft Performance Engines
Craft stroked 428 550 HP $14895
428 FE 428-463 Street Crate - Craft Performance Engines