After running a Wide-Band and A/F gauge it's become obvious the 1K's are mapped F A T and you have little risk of going too lean with STV holes. Removing them entirely won't throw off the mixture enough to worry..and in fact I think it moves it in the right direction. When I was drilling and tinkering with the mixture going by Seat-O-Pants it 'felt' better with a bit of fuel added in the midrange, but this proved in the end to be unneeded and actually way too rich.
My Assometer likes it rich, and going fatter always makes the throttle more responsive at whatever position you check. Problem is they're fat from the get go, and adding fuel going in the wrong direction. After 14K of running happily with the addition of a bit of midrange fuel the pistons and combustion chamber were heavily fouled with carbon. Funny thing was it always would return 50 mpgs even when running so fat, and this engine has impressed me with it's resilience to jetting being rich. It'll run fine even with mixtures so rich you'd think it would balk...but it just runs great.
The only reason we were drilling the STV's was being unsure of how the engine would respond to the additional airflow...which in the end showed it doesn't need the plates at all. Totally removed the engine mapping was fine (still a bit rich to be kind) and the engine runs great. It's a personal decision whether you like the increased power at light throttle that STV removal/drilling gives you, but we've not found anyone yet who decided to put them back in once they tried it with them out.
Advancing the timing does make it pull harder down low, but I think it only makes it more tolerant of the rich fueling and not because the combustion chamber actually wants more lead than stock. Once we bumped the CR to 12.5:1 and leaned the mixture quite a bit mine was tolerant of the 4 degree advance but pulled harder on the top-end with it set back to stock.
The TSCC type chamber doesn't need a lot of lead...especially with the CR up and I couldn't detect any detonation with the advance....just didn't pull as hard on top. YMMV but if you ever get inside the engine and close down the squish clearance (highly recommended) then retime the cams (again..good stuff) you'll likely find it runs just as well down low without the advanced timing and pulls free-er up on top.