Slant Six Headers
The only readily available slant headers (6 into one and 6 into 2 IIRC) are for the 67-up chassis and will not fit the early A's without a bunch of mods. Clifford sells the shortie headers (Clifford has a lot of bad reviews both here and at slant6.org - buyer beware!). They might or might not be in stock.
If your 65 has manual steering and is a 225, those shorties will fit. If you have PS, the only ones that will fit are the long discontinued long tubes. There's an outfit in OZ that is making the long tubes that fit with PS. If your 65 is a 170, then the shorties will not fit without mods. Headers show up both here and over at slant6.org on occasion but are snapped up quick.
Have you considered Dutra Duals? The scoop on them is available over at .org. Good luck in your search