Replacement Mobo for XPS 730 (not 730X)?

I have an XPS 730 that started locking up intermittently last fall. I diagnosed it six ways from Sunday, and never could get anything definitive -- it ALWAYS passed diagnostics. Then it got to where it wouldn't always boot. I ended up getting a new box (an XPS 8700 from Costco; I was desperate), but hanging on to the 730 (I love the case). My wife's OptiPlex GX520 is really sucking wind, so I thought I'd give fixing the 730 a try, but I don't want to put a lot of cash into it. It's still an older machine, but the Core2 Quad Q9450 in it (not to mention the fact that it HAS a video card) will run circles around her P4 650 (no GPU). For web surfing and watching video, it's more than adequate (the GX520 is starting to shut down more and more often with a "thermal event", so I figure it's near its end-of-life) This morning (first power-up in about 6 months), the 730's mobo stopped on a POST code of 4E ("Initialize APIC and set MTRR"). The next time I powered it on, it stayed up about an hour, till I shut it down. Then I disconnected the boot drive, just to let it get through POST, and it passed the POST 8 times in a row. Then I re-connected the disk, and, on the "Starting Windows" screen, it locked up (as it often did last fall). The next boot worked just fine, and I have every reason to believe it will stay up "for a while" -- I just never know how much of a while I have to work with, and it always seems to lock up at an inopportune moment, just before I'm about to save my data. This is what it was doing last fall when I gave up on it (I HAD to have a working machine, and it would run for anywhere between 5 minutes and 5 days at a time before locking up with no messages). I tried swapping out DIMMS, and the memory all seemed good. I ran RAMEXAM for days, and it never found a problem. Drive diagnostics showed all-good. Given that it DOES occasionally stop during POST with a code on the display, I thought replacing the mobo might breathe some life back into this old box and get me a few more years' use, as long as the mobo wasn't a fortune. The mobo says it's a "UU795" (silkscreened on the component side, near the DIMMs). I found a dealer that says they have a "DELL XPS 730 DESKTOP PC MOTHERBOARD F642F 0F642F CN-0F642F" for $119 (new; I suspect pulled from some units that never sold). I can't reconcile the UU795 and F642F numbers. Is the F642F a true replacement for the UU795? If it IS, then this seems like a cheap way to extend the life of what has otherwise been a great workhorse machine. Any thoughts or suggestions? Please don't tell me to get a new mobo and more modern CPU. I realize I'll be stuck with an older design, that an i7 will run circles around the Q9450, and that I'll be stuck with SATA II, rather than III, disk interfaces (for what it will be used for, that's more than enough) -- I just don't want to spend much more than about $100 on it. The last time I looked for an exact replacement mobo, the cheapest I could find was close to twice that; this seems like it might be the time to grab one. A new (modern) mobo, plus CPU, would probably be $400, and that's simply out of the budget.