Modify and measure. The Idea is too important to ignore....machine shop nation wide will get there becoming forchargeig so much and taking to longto complete our needs.
Considering a 4" boring bar is going to have a shank at least between 1-2" dia., good luck finding ANY drill press to handle it. Knock yourself out. Just don't ruin anything rare or desirable in the process.
Maybe you can run it on kerosene when you're done.