I have 2 of the 54b's just like yours bhinch & I use 50/50watt bulbs & have used them for over 4 years & have only had to change 2 out of the 4 bulbs in that time...They are so bright that I sometimes have others flick there lights for me to dim mine...I have have no problem with the plastic melting...Here is the link...
http://www.ebay.com/itm/Head-Light-B...item2a226c1c19