IMO, I think if you are already having issues deciding on who gets what you should just not do the loan at all.

If you are set on doing it I would only do it if you let him take first choice from the clutches, you get second, and then alternate from there. IMO, his pastel pied male is not reaaly worth all that much more than your adult breeder female Pastel het pied and spider het pied so I definitely wouldn't give up 70% of the clutch (not sure how you would figure out what 70% is anyway).

If it were me I would say forget the whole thing and just buy a male pastel het pied. You can probably find one for $500, you will still probably end up with the same amount of visual stuff that you would have got with the loan and you won't have to worry about who gets what.