It makes it easier to move the control arm when you are setting up the alignment having to use shims on the early cars and when you start adding more +caster, especially on a power steering car when you might want more then 2 degrees. you do not bind up the bolts in the holes. It just makes life easier for the guy doing the alignment with no downside to the slightly larger hole.
+1 on this. The arms will fit OK if you drill 1/2" holes, but when you have to pry them back to add shims (as you will with 65-66 cars), you (or your alignment guy) will be very glad to have the extra wiggle room.
"When a woman is a really good driver, she is just about perfect."
- Raymond Chandler
'66 GT Fastback show car, nightmist blue, warmed up original 289 & T-5Z, 3.80 trac-loc, AC, PS, pony interior, Retrosound, rally pac
'66 Coupe driver, Bullitt green, 302HO w/ 351W heads, roller rockers, Holley 600, T-5Z, 3.55 trac-loc, collapsible column, tank armor, disk brakes, shoulder belts
'11 BMW 335i X-drive, 6 speed manual, all the bells and whistles