I've made something north of 100 saws so I've drilled a few holes through varying thicknesses of saw plate & chewed up various types of bits over the last dozen years or so & learnt a few lessons along the way. I think you are over-anticipating the difficulty, drilling the two holes in your saw will not be a major problem with a decent new or fairly new HSS bit; typical saw plate is about 10 Rockwell points less than a HSS drill bit, a newish bit will go through 20 thou plate easily, but you certainly won't get many holes before the bit dulls too much to want to cooperate further.
You have several choices. The easiest would be to get a new HSS bit & be prepared to sacrifice it (if it's good quality it should still cut softer materials after two holes in thin plate but it will be considerably less sharp than it was!).
Option two is to buy the type of jobber bit with carbide tips which are meant for cutting all materials from plastic to steel (according to the pictures on the package). These are more accurate than masonary bits & will drill dozens of holes in saw plate with no problems (these are what I mainly use). Solid carbide bits are available, but not cheap, so unless you plan on drilling a lot of holes, not worth it. I discovered that you don't need lubricant with these bits when drilling thin plate, cutting fluid seems to speed up deterioration of the edge rather than preserve it (this is purely from personal experience, and I don't know why it's so).
Option 3 is to use a masonry bit - these vary in quality a lot, are usually not sharp enough to cut steel accurately and on thicker plate, can heat up enough for the tips to let go if drilling "dry", so I'd least recommend that route.
To mark out the plate for drilling, set the new blade in place carefully, then use an ordinary HSS bit in your battery drill to make an indent in the right spots. A couple of seconds with moderate pressure should give you a decent mark & is usually enough to start the bit without skating. You can finish the hole with the battery drill, but a drill-press is my preferred weapon, it takes a fair amount of pressure to make the bit bite & drill cleanly without over-heating (use a smooth bit of firm hardwood as backing when drilling).
You will almost certainly get a bit of flare on the exit side of the hole, which you can ignore if it's minor, but if your handle slot is a very neat fit, you may need to wipe the plate carefully over a stone to remove that.
For a two-bolt saw, you want to get those holes neat & accurate to ensure a good fit and the blade doesn't rattle about in the handle (nothing more annoying, imo!). The easy way to ensure you get as good a fit as possible is to mark & drill one of the holes, then set the plate back in the handle, insert a bolt, & mark hole #2. If one hole does ends up a bit "off" it's not the end of the earth, it's easy to extend it a little with a small chainsaw file. There are many, many old saws out there with over-large holes that are perfectly usable as long as the bolts are kept firmy twitched up, but you want to avoid that if possible..
Lastly - Tom, I've re-purposed many old hardpoint blades. Once you slice off the hardened teeth and about 1mm of the plate (you can see from the blueing how far the hardening extends, it usually survives for the useful life of the saw), the rest is indistinguishable from the saw plate bought by the roll, by my crude assessment methods (file-ability, 'spring' & wear characteristics). I don't know what alloy is typically used for hard-point saws but I have seen one manufacturer & supplier to the saw-making industry say they used 1080. Whatever they use, it seems to be hardened & tempered to much the same specs as that used for re-sharpenable saws. All but one I've re-purposed have been fine. Of the saws I've kept, I can no longer remember which is which & I certainly can't pick them apart in use, except this one that I made about 3 yrs ago from an Irwin blade (I think that was the brand). It gets a lot of use & stays sharp as long as any other saw I own:
(The shape of the toe end is to get rid of the "hang-hole"
I've only come across one example that I deemed a bit too soft - it was the cheapest of several hard-points that I bought purely to test how usable the plate would be. The 'soft' saw was utter junk, the teeth were so badly formed it would barely cut at all, & veered off to one side so much it was impossible to cut a straight line (all the teeth on one side were about 2/3rds the height of the alternate teeth!). Imagine some poor beginner trying to cut joints with a saw like that!
Old saws are not usually as file-destroying as the one you mentioned, but there are certain 'models' like the Disston 77 that are much harder than their regular line and certainly do a number on files, particularly the inferior files available nowadays...
Cheers,
Ian
