Millsy Iv'e haven't seen a credit reel on the 'Sweet Hearts', however from experience with similiar credit units on early 70's machines', I'm not sure whether you could increase the credit wheel credits. You would be windng the axle spring extremely tight and adjusments would need to be made to the posts on the cog which trigger credit limit contacts. May be able to wire up a light, bell or other. I would be interested to see what you come up with.

Regards
GT