The bolts are threaded into the aluminium, and where it is single thickness aluminium, they have nuts on the outside as well. All bolts are loctited. (The aluminium seems rather crudely cast, with huge grains and many "sinks", which implies low strength. Pressure cast aluminium tends to be brittle anyway, because high fluidity alloys must be used.) Bolting from the outside is viable for the bolts that currently have nuts, but not the ones that disappear into thick aluminium.
I was not attracted to aftermarket bases, for various reasons - probably mostly because they don't have Honda moulded into the front, but also because throwing $100 extra into a home mower doesn't seem sensible to me. I priced a new genuine base at $350: a lot of money for something so badly designed and made.
If the base fails again - which doesn't seem all that likely in suburban home service - I can still upsize the bolts and run them from the outside as you suggested, into the same brackets tapped out. Ideally I'd use heavy steel brackets both inside and outside, but that would look awesomely ugly. I may also mill out the trashed left front wheel area of the other (HR194) base shown above, and bolt in a replaceable chunk of aluminium, to take care of the recurrent chopping out of the left front wheel support. That problem is caused by the bell crank that the wheel mounts on: the single lever height adjustment system Honda uses is inherently a base-destroying concept. Note that the 4-lever base shown in this thread has all of its wheel mountings in as-new condition, despite seeming to have done even more work than that single lever HR194.
Incidentally Bob, that GXV140 engine on the HRU195 does seem to have had a leaky exhaust valve, as I guessed. (If I'd been wrong, I probably would never mention the matter again.) The seat was black all the way around, and so was the valve head in the sealing area. The whole valve head showed signs of overheating. Two minutes lapping with coarse compound cleaned it up, and when I tried it yesterday it started first pull for a change. I may have an as new engine that will last about 106.9 years in suburban service. Fortunately or un-, I probably won't.
