But should I do the leg lifting on MWF before/after a run, or should I do them on the lifting days?
It's hard for us to know what your leg strength goals are, but as you're pre-ocs, can we assume it's to add distance/pace to your run?
Under few circumstances should you start an intense leg lifting program on days before a run that same day. The reason I say this is straightforward.
Weightlifting tears muscles and builds lactic acid as part of their growth. If you ask these damaged muscles to support you on interval/distance at a pace, you increase your likely hood of pulls and tears. Additionally, a destabilized muscle could mean that you land wrong and damage joints and tendons.
A far better idea would be to incorporate leg lifts into your weight lifting days and remember that a little goes a very long way. What I mean there is high repetitions and low weight will surprise you with their effect. For myself, 30 calf raises with weight, 20/25 quad/hamstring lifts, etc are valid goals, with the weight adjusted accordingly. You'll also find that using free weights in things like kneel walks and box climbs becomes very very challenging very very quickly. Depending on how sore you feel, you might even do well to skip the first run the day after a legweight session.
NB, During a first week of incorporating legs into your training, you shouldn't increase your distance runs, pace, or interval training intensity.
Hope this helps.