rusted cast iron flange and toilet advice

Replacing the toilet in my grandmother's 1969/70 vintage home on slab. Pulled the old toilet out today and both bolts broke. The cast iron flange is rusted away to nothing and one side is broken off. I'm hoping it has just been set in lead but it could be in the cement. Ill have to clean it up to be sure. I'm unsure what I should do about a new flange. I know they have plastic and iron flanges that are suppose to tighten down. Or maybe I should go with one of those rings and try to fasten it down to whats left of the original flange. At some point the toilet had been tiled over so I will have to lay some tile to install the toilet correctly. This will be the first time ive replaced a toilet so any and all advice would be appreciated. Also I chose a kohler archer at my local home depot. Has anyone had any experience with these? My dad and I were looking at the kohler sante fe, cimmaron and archer.We settled on the archer.
thanks

There are repair rings that you can use to bolt in place. You may need a concrete drill and some lead anchors to lock it in place. If the inside diameter is 4", you could use an internal mount flange. It has a gasket that creates the seal (you need to brush and scrape off the inside of the pipe so it has a chance of sealing first), then expand it with the screws. After that, you still need to anchor it to the floor. The proper height of the flange is sitting on top of the finished floor.

If you check out Terry's first page, he has some toilet reviews. I have no personal experience with many toilets, but in general, the most highly preferred toilet here (and I have 4) is Toto. You won't find these at the big box stores, they're available at plumbing supply and other showrooms. Kohler tends to have expensive, hard to find replacement parts, and aren't the best performers.

Reports on this forum don't favor Big Box Store toilets much. Kohler has some models that seem to be OK, but many are not. Repair parts for some of them have to be special ordered from Kohler and cost almost as much as a toilet. Toto is the world's largest toilet manufacturer and all of their models for the least expensive to the most pricey have very excellent ratings. You may have to search to find a dealer, and even the lower priced models cost more that the Big Box Store's toilets, but they are worth it.

T o fix it properly, you can drill out the lead and pull the oakum, crack the flange with a cold chisel and remove.

Install a cast iron insta set and before pouring back the concrete, drop some screws down to hold it in place.

this is the correct way of installation. it will last for many, many years once done properly.

flange

I remove the flange and lead/oakum a new one in its place. I do not monkey around with replacement rings, or expansion flanges.

I appreciate all the advice. As much as I'd like to do the job right I don't have the tools or skill/knowledge to do the lead. Tried calling some plumbers and none wanted to mess with the lead either. Last one I talked to said "to much work". So I think im going to go with the internal flange. Just wondering what works best to clear out the deposits in the waste pipe? Im guessing wire brush. Is it safe to use a grinder on the remaining flange to get a level area? Sparks plus waste fumes seems like a bad idea. But maybe its fine.

Shouldn't be a problem, but removing the old flange should give you a fairly clean pipe to play with. I'm not a pro, but have removed a few. While there may be other ways (crack the flange with a hammer and chisel for one), I drill out enough lead to then pry it out so you can pull the old flange off.