4506 and 1006 frames and magazines are also made so that you cannot insert the wrong caliber magazine in a frame. I don't know but I bet a nickel S&W does the same with all .40s & 9mms.

I'd just keep an eye out for the next batch of police surplus .40 3rd generation pistols to go on the market. The last PD surplus I bought, a 4046, was $299 OTD. It was scuffed up but ran fine. Even if a 410 slide and magazines fit, building your own convertible you're betting good money that it won't turn out to be a jam-a-matic.