First determine how much total grain you're able to mash (counting the carapils and 60L), then convert the remainder of the 2-row to extract using a 1 to 0.75 ratio. For instance, if you're shooting for a 4 lb partial mash, I'd use:
.5# Carapils
.5# Crystal 60L
3.0# 2-row
The remaining 4.5 lbs of 2-row converts to 3.38 lbs (3 lbs 6 oz) of pale LME (4.5 X 0.75 = 3.38). That assumes a 65-70% efficiency in the mash. If you do a batch or two this way and your OG ends up a little low, you can compensate in the future by either using a bit more grain or a bit more extract.
FYI, if you use dry malt extract you use a 1 to 0.60 conversion factor.
1 lb grain = .75 lbs LME = .6 lbs DME
It's also important to figure out your mash and sparge water volumes based on the size of your boil pot. I usually do my partial mashes using a ratio of 1.3 quarts per pound of grain, figure out that total volume and subtract it from the size of my boil pot. That will be my sparge volume (up to 2X the mash volume, and I usually add about half a quart for grain absorption). I hope that makes sense...
Good luck!