Points gap for a 63' slant 6 225

I haven't used a feeler gauge in 40 years on a set of points UNLESS THERE IS ABSOLUTELY NO OTHER CHOICE

1...Bump engine so points are open on cam. set "by eye" so they are "I guess" about right, so they open and close.
2...Inspect cam make sure it is clean smooth and not rusty.
3...Make sure you have a SMALL drop of proper cam lube grease on "entry" side of points rubbing block
4....Hook up your DWELL meter and crank on starter to get a reading, with coil wire grounded
5..."Guess adjust" points. More open = less dwell, more closed = less dwell

Dwell spec is 40-45 YOU WANT IT ON THE low figure (more open) side, because the rubbing block will wear closed

6...Recheck dwell with engine running. Set dwell FIRST and timing SECOND. Dwell affects timing

IF YOU do all this right, IF THE distributor has not worn, IF THE dwell and timing were both correct at the previous tune-up, you will not have to change the timing