Stripping Down a DEC Professional 350

I have had this machine for a while now and decided today to at least start cleaning it up. It is very dirty inside. The trouble is I can't see how to get at the motherboard, which I can needs cleaning; it seems to be under a riveted plate and I can't see any way to get it at it, or even just to remove the cover for the option cards. Is there a trick to this that I am missing? I have looked around for manuals, but there don't seem to be any online. I am also unsure how to remove the option cards, do I just turn the plastic knob clockwise? It is stiff and I don't want to apply too much force and break something. I also just noticed that it is missing the power switch, don't suppose anyone has one going spare? It looks like probably any DEC rocker switch would be OK. You can see the type I mean by looking at this http://www.recycledgoods.com/zoom.aspx?productID=19036. Incidentally, I opened up the PSU to clean that out. It looks pretty bad: there are quite a few patch wires there, extra components clearly added after it was built, components that look poorly placed, two resistors soldered together in series by their leads, an inductor soldered with large blobs of solder that look worse than anything even I could do. I am left wondering if this typical of these PSUs or if I have just got something that has been hacked about. Thanks Rob