Ram Air IV versus 455 HO

[supergonzo]

"I would recommend a Hyd roller possibly a Comp XR276HR or a XR288HR "
The 276 would idle just fine. The 288 will be a little lumpy, with about 14 inches of idle vacuum. But will give you more upstairs. If you are looking to just drive the car without ANY headaches the XR276HR would be fine. You do not need to modify the lifter gallery. But you MUST buy the whole Comp Cams kit including pushrods for you to not run into any geometry problems. 1.65 roller rockers would be great with this setup.
I had this exact Camshaft in a 400 RAIV car, and it idles fine, and runs 12.50's (with headers & stock quiet mufflers) all day long.
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On a previous note: The RAII heads were not exactly the same as RAIV heads with a different camshaft rocker arm ratio. The RAII heads had the same intake openings as d-port heads, much smaller then RAIV intake openings. However because of this extra casting they can be ported today very well.