Dan, that 105 Xenar was a lucky snag indeed. It is a normal lens for 2x3 (nominal 6x9). Even though I'm a strong fan of the 101/4.5 Ektar y'r Xenar ought to be pretty good. Neither is fit for use on 4x5. There's a reason why they cost so much less than, say, 100/6.3 WF Ektars and other ~ 4" lenses that really do cover 4x5.
I've bought one Sirchie camera so far. A mugshot that looked like it was 2x3, turned out to have a 2x3 Graflok back (Sirchie made, not easily used on anything else) with a regular Graflex-made 2x3 focusing panel and a sliding back that actually takes two shots, slightly smaller than half of 6x7, on a 6x7 frame. Copal Press #0, which is why I bought it, and a 105/4.5 Comparon that turns out to be fairly good as a macro lens. Nice thing about it being in a #0 is that it can be reversed by swapping the cells front to back.
Cheers,
Dan