Are the holes in an oil area?
If not, I'd get a soft plug to fit like the big block timing hole plugs. They'd look like someone had intended it for some access reason.
If they are in an oily area, I'd still use the plugs, but I'd coat the grommet part with some gasketmaker sealant. I had a similar sealing issue when I added a PCV valve to a Convert timing cover, vertically, beside where the pump casting is. I only mention that because it's a location above the oil level and not in the same chamber as the thrashing crankshaft. It's indirectly attacked by oil, mostly mist. The first time I installed the PCV soft grommet dry, hoping the expansion from the valve insertion would make the seal. It did not. Next time I used Permatex "Ultra Gray" gasket maker. It's been dry since.
So I'd think that if you cleaned up around the hole a good plug would fit well, seal well, not look odd, and the cost of the sealant will exceed the cost of parts (There's your guzzi content).
Don't use RTV there.
