Morepower, I stabbed a 408 LA stroker into my '62 Valiant V-200 more door back in 2003. It's a pretty tight fit, I think because the "early-early" A body ('60-'62) has a narrower engine bay than later models had, but otherwise a fairly easy engine swap. I used Schumacher 225 => LA conversion mounts, but I'm not sure if they are still available. I also used a Schumacher torque strap. I had to get rid of my heater box, and the Schumacher mounts put the distributor right next to the firewall*; however another FABO member did find enough room for a modified heater box, probably using different mounts. I did not find enough room in the engine compartment for the battery, so I relocated it to the trunk. But again, at least one other FABO member did find room for the battery in the engine compartment. (I'd suggest that you search the FABO archives for those threads.) I am using stock exhaust manifolds off an early Duster 340, and I can get you the part numbers if you need them. Due to the narrow engine bay, I don't think there is room for headers (especially if you have Torqueflite push button cables running down the driver's side of the engine) unless you cut the fender wells.
I think you should inquire on this board about the difference in width between the '60-'62 engine bay and that of later models. (Assuming you are using a 904 transmission) there might be room for headers if you used a manual valve body and got rid of the shifter cables. You might have to get a different transmission because the slant 6 and LA engine versions of the A904 have different bell housing bolt patterns.
*That's a feature, not a bug! Michael Schumacher is a racer-type guy, and I think he wanted to move the engine as far back as possible for better handling.
