IMO, 421/435 is too far off to be even a worn out 340 stick..
The 410/410 is a 360 2bbl cam. IIRC that is a 252/260/111 cam with 34* overlap; works good in a 318LA with the 360 springs;
And shaved heads.
Or with just a 2800TC,
or both.
Or could just use closed chamber heads. But super with the 2800TC.
That 2800 makes a sweet 318LA no matter what,lol.