I have done three engines with 3/8ths pushrods so far--no grinding needed BUT--I did take my time and shim each pair around like you always have to do on Mopars--these were all rollers as well
Maybe you need a touch here and there--it would be a big plus to have just a tad more room then it would be for sure but I think any engine builder that knows his way around a Mop will have almost no trouble with 3/8ths--