6.1 Swap into a 68 Dart

Don't believe you will be able to use the 6.1 exhaust manifolds. Not without some kind of steer by wire setup anyways. :)

Here is a thread on PS delete - 6.1 no p/steering no a/c pulley

If you want to keep your AC pump, I think you will be rolling your own DS mounts. Not even the Holley swap mounts allow for the low mount AC compressor on an early 5.7 or 6.1 and they move the motor forward like 1.75". You could try and make a truck timing cover work (pretty sure it would bolt on) which puts the AC compressor up high, but I doubt you will be able to run the 6.1 intake then. Maybe you could try a later truck intake? I think the ports would work, but not sure how the alternator mount and intake would interface.

Only other options I can think of to keep the AC is an aftermarket suspension kit.

Might be worth thinking about an Eagle (VVT) 5.7 with the Holley swap parts. You will have to probably run a cable shifter for the trans but they at least have a mount to go with the relocated motor. And you will need a v8 k-frame if you don't have one. But this will keep your AC compressor and the later motors have a bolt on PS delete bracket that is a factory part. You won't be down much on power, a cam swap would get most (all?) of that back and you could run your 6.1 intake if you wanted to keep the 6.1 look. Just an idea.