352-
Oh hell, that's not as bad as I thought the problem was. I figured, knowing what I've seen in my past, there were going to be a couple of good- sized cracks, or even a portion of the casting missing. Don't ask me how I know. This is why I'd asked if you needed one of the inserts.
It looks like this is a good candidate for your die grinder to relieve some of the metal so you can lay in a pretty good bead. I'd get in on both sides of the crack, on both sides of the case, and cut it back a little bit- but I'm sure you're hip to this already, working with the welder and all.
That's a quality casting- I'm not picking up any visible porosities from your pictures, so that's going to make your cleanup and welding a bunch easier. Still, cleanliness is godliness and a good, trouble-free weld here. Can't stress this enough. Tapped holes are always a bitch to redo, especially if the previous repairs have been a combination of RTV, threaded inserts, JBWeld, and whatever else mixed with oil. Again, don't ask me how I know.
Make yourself a lineup setup, and let it be known that you've got 'em. You'd be amazed how many problems like this there are out there. And hell, you're on the west coast, so we won't be stepping on each other!!
Rings aren't the only thing you'll need to think about. Among other things to consider are, in no particular order- (just how they failed in my order!!!) piston to jug clearance, serious valve springs, cam, fail-proof ignition retard, among others. If your're going to double plug the heads,(EASY) you've got to get the right coils and go with the single fire ignition. Bet you've got that ignition already, though. Best single investment for a shovel. One thing that's great is a lot of people have done a lot with NO2 now, where back in '84, there were only a couple people sick enough to think about this, much less try it. Like I said earlier, I blew a couple three motors trying to get the setup dialed to the point where it is today.
I've always used the thoriated 'trodes in my work. I work a small 'pool' down the crack, it's just been my experience that I want to work a small, thorough weld rather than just blast a huge pool and have the workpiece "sink" around where I'm working. Your technique may be different and you may be a better Al welder than I. All I can tell you is what suits my particular style.
Billy