Well some progress even if it doesn't sound like it. Thanks to those who commented on my question. I finally encountered some "truth in advertising", as I discovered a distributor's notes to the effect that a particular Code reader didn't read Volvo, as well as certain other European marques. This is the sort of thing which I'm looking for at the moment, because it affirms what I had feared, that they'll brag that the article fits all, but it ain't always the case. I guess I'd better head south (of the border) and prowl Bellingham awhile to follow up on advice to try and find an item among the loaners, that works; up here, most (of the few) service outlets aren't really into giving out free diagnostics or advice, and the rest have the dealership proprietary analyzers, which won't help me in my quest for a DiY's apparatus.
If I'm successful, I'll post it - there must be at least one other '98 V70 out there whose owner has the same aim as I, not to mention the same constraints in terms of cost.

gus_boy