I believe the stock spring set upon the al head is 1.780".

 

yes that is "installed" height. The heads themselves are cast "about" 1.750 ish and shims are used to make up the difference to get the spec 1.780" height. You will notice some springs have shim(s) and some don't to get that height

My $02 is just use a valve spring height measure tool and use .xxx shims as needed to get correct height. Many aftermarket springs are spec 1.800" so likely no shims are needed on heads that have not had the spring pockets machined down and on some valves they may actually be installed at a tighter spec which increases their seat & open pressure above advertised LB rating of a 1.800" height. "Ideally" you want all you springs installed at the same height so valve spring pressure both seat & open is consistent between each cyl.

 

You're first sentence is incorrect. You can't use shims to make up the difference from 1.750" and get 1.780", it would be the other way around. Shims are used to reduce the installed height to achieve your goal. The al head is finished out about 1.810"ish. Add the .030" required spring pocket and get the 1.780"ish with the stock hardware.
Most people use the +.050 lock along with some shims to get the 1.800". It's a lot easier than machining the spring pocket.

 

yes,lti...I had it backwards. meant to say the head casting is cut larger than the 1.780 as you noted around 1.8xx ish. If 1.810 than yes the .030 locator alone get the "installed height" at 1.780. if the milling was slightly more than 1.810 then a shim of .xxx is needed to bring it to the 1.780 "installed" height.

thank you for correcting.