The good news is: Your cracks seem to avoid the main race bore. A competent welder can stitch it up with a minimum of distortion if his fixturing and oven are in order. Occasionally the correction on the main bore is within the limits of in-line honing for oversize rollers. That is a cost you would properly encounter with a blue-print rebuild anyway, and more if an aftermarket case is to be matched. Worst case scenario would be to have the race bore line-bored to an oversize (Jim's Machining supplies such a race) to assure perfection, with perhaps some decking and spigot clearancing for good measure.
If your machine is nostalgic and not rad, you will probably find this route to a repair more satisfying in the long run, for 'originality's sake'. If you are into HP and breathing fire, then maybe modern metal would be more appropriate.
[This message has been edited by Cotten (edited 12 June 2000).]