[V8] off topic - big SUV tire ?

[Scott Baumann / Progressive Technology Solutions]

Question for any tire experts out there:  
I replaced our venerable '97 Expy EB at 260K bulletproof miles with an '03 Navigator.
The tires on it now are 275-65-18.  I have an oppt'y to buy some 275-70-18's for a deal, 
and am curious if there may be a fit issue.  TireRack and tires stores are pretty useless,
other than to tell me what was OEM supplied.  Thanks for any thoughts!

Scott Baumann

'90 V8Q @ 184K http://198.107.18.114/V8Q/Paint/LY9B.jpg (thanks for the URL Jeremy Ward!)
'03 Navi Ult @ 29K