Exhaust Manifolds

Probably part of it, but also 340/360 builds are fairly straightforward and established what to do, 273/318 there's little consensus about best way forward especially since a large group of people see no way forward other than barely touch it or a 340/360+ swap.
Myself, I probably wouldn't do a 340 /360 swap if I already had a 318. To do the swap there's the expense of buying the other engine, 360's are balanced differently so there's the extra cost of a converter LA 360's. The motor mounts are different than the 318's. I'm not complaining about the cost, just stayed what's involved.