Lost Frost plugs

There is no such thing as a "frost plug". The American term for this myth is "freeze plug". Engine blocks have "core plugs" which people mistake for "freeze plugs". A core plug is an artifact of the casting process used in the manufacturing of the engine block. For casting reason the block needs a couple extra holes which are then sealed with core plugs. The holes are not there to prevent freeze damage and indeed won't.

True "freeze plugs" do occasionally occur in large engines but in a typical passenger car engine they don't exist, though nearly all engines have core plugs.

Hopefully your engine is still good. I agree with the brass plugs and I just ordered a kit for my engine which had every plug I needed and some I didn't. The complete kit was under $10.00.

Edit: Looks like the price has gone up about $5.00 since I bought mine.