I have a 73 Chrysler that has the 400-auto trans that I’m thinking real serious of swapping both into the 65 Sat. (The 273 is old and tired) my main question Was it an unleaded head engine being a 73? I’ll change steering column out for an extra 66 I have that uses the rods not cables so no problem there. The paint is wore thru in places so it looks rat rod cool, be neat to find an old taxi or store stencil to put on doors.

does it have a cat in the exhaust system ?
if so, that indicates it requires unleaded.
my old man bought a 73 newport new, but i don't remember if it had a cat or not. it had the 400 engine as well, but the old man always bought the cheapest gas available for all his cars, no matter what was said in, or on [around], the gas door or cap.

You will need the early B motor steel engine mounts and the rubber mounts for that K member

I think so. The heads are #346? They're mostly the same as a 906 head, but with induction hardened exhaust seats. No cats on any US cars until 1975.

I had those in my stash for many years waiting to use, debating on exhaust manifolds, the logs that on it now or 69 hp type. It has 2 barrel on it now but I’ll change to a 4 barrel and intake. Would like to find the 68-70 hp cam too. Probably have to make a driveshaft to fit from that 73.

Haven’t looked at numbers but thinking they might be the same as the 74 440 I have.

I'm pretty sure the "346" heads were one year only for 1971

The 346 head was late '71-'73.