I agree with this route. See what you have to work with first.
My opinion is moth ball the 273 if its the original motor and build a 318 or 360. But it all depends on what you want out of the motor, intended use and budget and in this case the budget. 318's are a drop in with the 273 accessories and pan, abundant, cheap, and you can get a Magnum block and go hydraulic roller, and you can still say "I have the original motor".
