The aluminum frames really aren't much of a problem if you use some common sense. The big problem area is the recoil spring guide seat just ahead of the feed ramp. Simply using one of the elastomer or nylon buffer pads between the recoil spring guide and the frame will almost totally eliminate frame cracking.
Just between you and me and the doorpost, almost all cracked frames I've seen have been accompanied by noticeably beat out locking lugs on the slide and barrel, which means the guys have been trying to run "magnumised" handloads through the things.
I do recall seeing a couple of the early Colt alloy frames though that seemed to have just plain let go on their own under normal use.
Y'know, the frame could also be split into a fore and aft configuration, parted right down the mag well. that would simplify a whole lot of the machining and the left side top rail could be joined by a beefed up and screw mounted p-tube, with a similar tie plate on the right side. A well designed magwell could be machined as an integral part of the front section and an extra long mainspring housing pin used to tie the bottom ends together.
EDIT> I'd be real leery of the lengthways split on the slide. Any way you go about it you are going to force heat treatment of the assembly after welding, since you'd have to have penetration weld right through the lugs and would end up with hard spots not to mention making yourself recut the lugs after weld/HT. If you don't have through weld at the lugs, you can count on the slide letting go at that point, as the load bearing section would be drastically reduced and the load split to the two sides, leading to "pull apart" even if the lugs are dead nuts square to the bore.