318/360 production info

Most all "LA" 318 and 360 are pretty much the same. Except for few applications their mainly non performance oriented engines in stock form. The 360 heads have bigger valves and bigger ports and it will have different motor mounts then your 273. The newer Magnum engines would be a nice upgrade but it's not a direct swap. Go here find out more about the differences: LA - Chrysler small block V8 engines
And here for more information on using the Magnum :
Required Modifications

By the way why do want change out your 273? Is there something wrong with it?