How much does the lash change from hot to cold, if any? Iron block and heads.

.004 from cold to hot with alum heads

About .002 looser with iron heads and block is what I count on
On your deal check it out for yourself on your parts, set them cold and then go drive the car enough to get the oil temps up to at or above 150F and pull the easiest valve cover off and check one set of rockers quickly the same way you set them
Not all motors do the exact same thing under the same conditions, iron rocker compared to aluminum changes things also

Thanks, this is a 340 stocker with the hyd cam and Schubeck solid lifters and the lash will be close, .002-.004. So I guess setting them hot should be the only way? No short cuts, oh well. From what I read on Class Racer that's the lash they recommend.
What's the time window for settin hot before its to cool?

We see this question month after month here
There is no way to set lash properly other than setting it Hot Period -- all the "predictions" of what to allow with this and that combo is BS or at best is based on doing it both ways and comparing which is just crazy do it HOT
and in your situation it is the only way to even get close
You will find that is it almost impossible to set lash that close
any other way and for most folks they will be lucky to get it +- a few thou
Set it as hot as you can get it---also on those kinds of cams the "low" spot may not be in the location you assume IE inverse radius designs etc--If lash specs call for that close you need to set hot then roll it over on every one a full lobe rotation and see where the base actually is while you have feeler in place
Truth is it will run great no matter what you do they just have to give some kind of spec and they are shooting for you getting the most out of the lobe
Your burn out is probably way more important as well as about 7 other things to getting a win light

Thanks, I was thinkng of setting the dial indicator on the lifter then moving the cam to find the low spot, but the feeler in place is a good idea. Hot it will be, I can see your point on that. Big learning curve on this whole package. If the car runs at all I'll be happy.

Don't over think it
She will run great!
Good Luck!

We do a bunch of 22R Toyota engines--they have an odd inverse radius cam lobe profile and setting them requires just keeping the blade in place and rolling it over and over so i really learned this trick doing "terrorist trucks" LOL