TJP, I did this swap (LA 360) into my daily driver '62 Valiant V-200. The pre-'64 A-bodies have a quite narrow engine bay.
The K-member on the '60-'61 models is Valiant/Lancer only, but in '62 they started using the same K-member in the A-bodies as they used in their other cars. So a '62 is definitely easier for this swap than a '60 or '61.
I used Shumacher conversion engine mounts, which work well, but they move the engine back on the chassis as far as possible, so you have to ditch the heater box. However, I believe Hemi Demon fabbed his own mounts, and was able to keep the heater:
Engine swap 62 Valiant
Hemi Demon was also able to find room under the hood for the battery, but I was not, and had to relocate it to the trunk.
I used exhaust manifolds from a 340 because they were the only ones I could find that would clear the fenderwells, but my engine has a fairly large cam, 10.5:1 compression and is ported, and I think those manifolds are too restrictive for my engine. I haven't figured out what to do about that yet. With headers I think you are talking about cutting the fenderwells.
I swapped in '72 Duster V8 front spindles and Kelsey-Hayes front disc brakes. In the rear I am using the 8-3/4" diff with a Dana Power-Lok posi and the 10" drums from that same Duster.
I hope Hemi Demon chimes in here. I am sure he could help you a lot.
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