After tune up, hard to start

[swissarmychainsaw]

Hey folks!

I'm teaching my 10 year old how to be a gear head squares junky. So far so good!

1973 Suburban 350/350. GM HEI ignition (likely from an 80s era truck).

Had the truck about 5 years and never did any tune up on it.
It has always been very easy to start when warm.

Cold (after a couple days sitting) it would do the typical "crank, crank, crank - where's my gas - crank, vroom"

Finally started to miss, and was not running on all cylinders (all the time), so we replaced
* plugs
* Plug Wires
* Distributor Cap
* Rotor

After my "tune up" it's been not wanting to start when warm, and requires several seconds of cranking.
So I've been fiddling with the timing a bit.
Assuming that when you do cap and rotor you have to reset the timing

I unplug the vacuum hose from the distributor vacuum advance to do this.
Warm it up, then set "initial timing" (at idle).
Originally I put it at about 14 degrees BTDC, (hard to start)
and today I bumped it down to 10 degrees.

What should this be at, and will small differences (say going to 11!) make a big difference?

Thanks! I really want this thing to fire right back up again!