yes. but you will have to yous the old seal from the 1969
no.
If the 71 is a standard then yes it will fit.
yes
No they will not. Only 1970-1972 doors will fit on a 1970 Chevelle. 1969 is only interchangeable with 1968.
69mm.
No it will not.
Yes
Yes a 429 would fit into a 1969-1970 ford mustang without no engine compartment mods
yes it will
Not without modification
No only 1970. 71 and 72 are interchangeable
the interior door handles changed in 68' so the door will probably line up but the internals might be a bit whacky