Steptoe, the Briggs engines normally have a full-floating gudgeon pin, which means it is located axially by circlips at both ends. The pin can't move toward the bore unless somebody had left out the circlips, or put them in so badly that they popped out, during a previous overhaul. (Most of us have probably seen this happen, however - I certainly have, with car engines.) Hence end float of the crankshaft, or lateral slack of the big end bearing on the crankpin, should not result in score marks down the bore.
If it has a scored bore, I can't understand why you don't just salvage a few parts and throw the rest away unless it is a rare model of interest to collectors. The cost of reboring and buying an oversized piston greatly exceeds the cost of picking up a better Briggs engine from a nearby nature strip. It can't operate satisfactorily with deep scores down the bore.
