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Good choice! Only I would just buy 427 390 horse decals; not build or buy a 427 (unless we are talking about an LS-7 seven liter fifth gen small block). Instead I would build a 496 for your '63. They all look alike on the outside, and a big block really wants a LOT more compression than today's pump gas can support.
A stock SBC 400 can out compete a 427 (and probably a 496) on pump gas in all performance tests. It just won't have those mile wide valve covers.
You can blame the engineers that designed the BBC in 1961 to run on 104 octane gas. They had no idea that unleaded 87 octane swill was on the horizon. The head design (a modified Hemi chamber) requires high static compression to work. Take away those huge domes and replace them with a dished piston and the fire literally goes out before all the gas it inhales is burnt. That is what makes it a "dirty" engine and banned it from cars in 1971 (1969 in California).