I have used masm 32 bit successfully before. Going by the documentation for ml64 I expected to have similar success with ml64.exe. However, PROC doesn't give me parameters as expected. All things work per the x64 ABI but I don't get any help from masm. It looks like PROC isn't treating stack frame parameters / registers as per the ABI. I am new to x64 so any information would be appreciated.
forget ml64 - a lot of MASMs highlevel features were removed. Instead use JWASM: it is support all well known syntax elements from ml and also extend it for x64 requirements.