m386b4g70bm0-yk00 is LRDIMM and PowerEdge R420 does not support LRDIMM. You can refer below link for supported memory for PowerEdge R420 [URL] 
Thats it pretty much, once I gonna buy these online and refunding isnt an option, I cant miss. I gonna buy 2 of any of these memories to use 1 module in A1 slot and another module in B1 slot, 2x32gb. [IMAGE]  
Need help finding out if the following memory modules are compatible with R420