904 Transmission 1-2 shift control valve spring install help.

That's sorta what I did.
But don't go crazy on this cuz you can hold it in gear longer, in manual mode. If the auto upshift rpm gets to be too high, it kindof sucks around town.
I lowered my 2-3 instead,to better balance the shift rpms; then screwed around with the line pressure and governor to fine tune it.
But don't go crazy on these either, if a streeter, cuz too early auto downshifts suck more than not soon enough ones,lol.

To make line-pressure adjustments easier on the 904, I drilled and tapped a hole for a small pipe plug, in just the right place, which you can see where to put, with the pan off. Now you can scoot under there any time and give her a twist.
Don't forget to synchronize your KD linkage, and there are a couple of different levers you can bolt onto the trans to vary the throttle pressure ratios.

Personally,in a streeter, I like a slightly earlier 1-2 shift with performance gears, as long as the KD mech is working right;
but not 1000rpm earlier,lol.If a streeter,don't go crazy on these, you'll just wear out your creeper.
If a streeter, that's why the PT kickdown was invented, and what the manual shifter is for.
Happy HotRodding.