Yes, your compartment is too tight without modification. So.....there is another "stickie" with photos as well as a great write-up specifically about converting 2008 and older Precedents to 8v batteries. Its a number of pages long but is very specific. If I buy an older Precedent, that is what I will be doing.
See:
http://www.buggiesgonewild.com/elect...-part-1-a.html