I had replaced blown head gaskets on a 500c.i. engine
a little over a month ago.
The Heads are Brodix Plus2 CNC which I had resurfaced.
The machine shop took 20 thousandths off of them.
Will I have to have them resurfaced again in the fall when I rebuild the engines?
If not what's the best way to clean up the surface?

wouldn't you machine guy determine that ? If they are not flat it has to be done ......

I've always had them resurfaced when the heads come off.
Machine shops always resurface as part of the program.........

On all aluminum heads, the old head gasket will always brinell or leave an indention in the head where the fire ring is. I would never send them out without milling. We only use a CBN mill machine on all heads,and yes there is a difference.Machines that have multi carbide bits will not get the RA finish that the CBN (cubic boron nitrate)bits will. Also the older machines that have CBN converted bits do not have high enough RPM's to do the job correctly. The better the RA finish,the more gasket to cyl head contact, the better the seal. But dont take my word for it ,call any gasket company and ask them!!! Also if your shop guy has a good machine he will not have to take .020" off which will change the cc volume of the combustion chamber which will change compression ratio. We have taken as little as .002" to clean the surface up............KR Hawk Marine