Combining igf w/slin can be very dangerous as they work synergistically to lower blood glucose levels. You're really going to have to decide for yourself whether or not the risk is worth it. If you do decide to combine the two start out w/a very low slin dosage like 4-5 IU's.
Also I would use the igf alone for a couple of days just to see how it effects you. For some people igf use causes them to go hypo, this is something you want to know before the addition of slin.
Something else to think about is that most people like to take their igf right after their workout in whatever muscle group was worked. If you're working out at night definately do not combine the slin w/your igf. But for non-workout days or days you can train during the day you should be fine. Just be very careful bro and start out very low w/the slin dose.
What's your experience w/slin been like? Dosage, how'd you feel, what type of diet plan do you follow when you use slin?