Early A V8 swap advice

As to headers
I highly recommend not to try and run the long-tube under chassis headers.They are hard enough to fit with an automatic.
By the same token, I ran Hooker fenderwells, the only game in town in 1975, and while they offer great accessibility, the lack of room in the wheelwells really limits your tire choices up front, and in turn,that really limits your handling.
It seems to me there is one manufacturer who offers a 3 down and 1 around for these cars. That is to say 1 pipe goes thru the apron and down the outside of the frame rail. That seems like a reasonable compromise. I have no experience with this header and cannot recall the name of the manufacturer. I myself would like to try it.