Yours is not the 340, obviously. Looks like that one had a 80586 (with built in FPU).

Still your card might fit in an (earlier) 3X0 series.

If there is a VGA conector on the card, a seperate monitor should work instead of the multiport thing.

Had a similar setup with my Amiga2000 and a 80386 card with a display selector switch.

I would cross-post at Macintoshgarden, some people over there may recall about orangemicro stuff.