The drivers sides of the motor mount bosses on the 340 and 360 blocks are either wider or narrower(CRS) than the 273 and 318 blocks are.I have seen racers use flat washers as spacers on the wrong mounts to make the motors bolt in the chassis they where working on, if you have the correct year 273 mounts for your car you should be golden
Worst thing is you may need to have that side modified to make it fit the way you want it to
I have a 1965 dart 270 that I'm making into a S/P car with a BB in it, it still has the stock inner fenderwells so they may end up being removed for the headers
Not sure yet, I'll slide the motor back as far as I can and not cut the firewall up to make it fit. IHTHs