I've done several blocks through time. I prefer a 5/8 OD copper tube. I've also done a few with a thin wall 9/16 copper tube, its a little thin for me. The tip about the tube fitting slightly loose is great advice. I've purchased my bits and reamers through Mcmaster and had an extension welded. When redrilling the oil galleys take the time to drill them slightly oversize. I think the original instructions called for 9/32 I've done most to 5/16. Be careful with every step ! When peening the tube I've used a ground lifter for the first trip after that I've used a broaching tool from Goodson that works very well. It may take some work to get the lifters to slide in the bore. I've also used an adjustable reamer in the lifter bores to get everything where there was no binding or tight spots. Be careful not to get the bores oversize. At one time there was an article in tech archives by Herb McCandless that was very good. I have a number of Mopar performance articles covering this modification. PM me as needed. If you're using push rod oiling both sides can be tubed but the lifter bores will need an oil feed hole and you'll need the special Mopar tool to do this. I have an X block done that way.