afaik Olympus OM lenses will only work on Canon EOS and fourthirds cameras because the sensor to mount distance has to be significantly smaller than on the OM mount...
There are no cheap Canon DSLRs available with a good focusing screen (maybe you can get a used 1D but that could be quite overkill and is not really cheap) and in fourthirds world the old Olympus E-1 would give you the best screen.
I use OM 50/1,4, Vivitar OM 100/2,8 macro, Tokina OM 400/5,6 and OM 20/3,5 ultramacro lenses on my E-1 and i can focus them manually (I prefer the viewfinder on my E-1 for MF over that on on my previous Canon 10D).
I would not recommend the optical viewfinders of E-300, E-500, E-330, 300D, 350D and probabyl 400D and E-400 for use with OM lenses.
My suggestion would be the E-1 but you need at least a new fourthirds wide angle lens because of the crop 2 with your OM lenses...
On Pentax you only have close focus, on Nikon (D50-D100) you only have close focus and no metering with OM lenses!