Get the right parts and valve body and for a street car, even a stroked street car, you'll be fine. Especially if you plan on running street tires.With street tires you'll never load a well built 727 enough to hurt it. It won't be scared of drag radials either, cause they won't dead hook on the street either with a hot stroker. It would take a lot of torque, stall, and traction to even start to threaten the integrity of a well built 727, no matter the cores humble beginnings.

I have had both 3 and 4 pinion planetary 727s behind my strokers on the street and strip with drag radials for many years and have never hurt a planetary. The best advice above is to go with the core you can find with the least abuse. That is probably more important than the number of gears, at least in my opinion and experience.

P.S. Where are you located? I have a dozen or more good BB 727 cores that I will never use. Some from passenger cars and some from trucks/,motor homes.