I might go a little more recent unless you already have a good selection of M42 mount lenses. Look for a Pentax KX or K2, the metering on these is much more accurate and it's open aperture too. The K2 was their first production model with an electronically controlled metal shutter so the speeds tend to stay accurate and it makes a lovely solid "crump" noise when you press the button.
I have a couple of SPs and while the build quality is first rate they definitely need attention after so many years. My KX on the other hand has had nothing but a clean, new light seals/mirror foam and some tweaking to make the aperture display window work. It still seems accurate enough for slide film at all shutter speeds, judging by the rolls I've had back from it. The K2 has had a bit more work to straighten a bent hotshoe (turned out the top plate was dinged, so took that off and beat the dent out) and replace a broken spring intended to hold the winder lever against the body but the meter and shutter both seem very accurate.