I have done freeze plugs on various vehicles over the years and used permatex, gasket shellac, and even wet spray paint. Basically anything that is non-soluble and a little sticky to seal any little roughness in the block holes, at least with steel plugs. Brass plugs are likely soft enough to just go bare and fill in minor rough bits. Since I posted a pretty shade tree solution someone will likely come along and give 'better' solutions.

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1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)