###284* Purple shaft too big for stock lo-po 273????

Yes.
-Way,WAY too big, for street.Your dynamic c/r will fall into the basement, making the bottom end(take-off) really soft. That coupled with the stock TC and 2.76 gears, will make it feel like its a 4 cylinder. And the MPG will be atrocious. How did this idea get into your head? That cam is even big for a stock 360, and maybe even with the c/r bumped up.
-Now if youre going to spend more than a little time at the track, different story.But you will need to pump up the c/r in any case.Or if you take a lot of weight out of the chassis.......
-Focus.
-Theres nothing wrong with that 273, as is. If you want more power put a bigger motor into it. Even a stock 318 will be more satisfactory than the big-cam273.If you really want to keep the little stock 273, consider a 4bbl and dual exhaust as the limit.With maybe headers and/or 3.55s as viable options.
-You know that engine is at least 45 years old,right?
-And then theres always turbocharging.Could make that little puppy pull like a 400.