I have a nice 454 in my car. I think I have around $3k total into. Everything was rebuilt or new. It's nothing special, 781 heads, 10:1 CR, mild Sealed power cam. Has a nice idle, but not a fender shaker. Just enough to make it sound good and turn some heads. It has manifolds off a truck, made like they were for the car. I have a 4-speed in mine, not many options for headers. Also didn't want to deal with bottoming out. I have 2 1/2" all the way, H pipe and fake Flo's.
Car has plenty of power even with 3.08 gears. First gear in the Saggy could be a little more, but not bad. Still can do 70+ without the engine screaming.
A big block will drop right in. Use the stock clam shells off the 305, use manifolds, low profile valve covers, and an aluminum rad can be had for under $200. Mine is just a driver, will never see a drag strip (other than the parking lot) but I like big blocks. Everybody has a small block.....