and am wondering if they will fit my car, with the stock tires.
The company stated that they couldn't guarantee the wheels for my car because they are 5 X 120 and the pattern on the XLR is 5 X 120.7
Welcome to the XLR Community.
I don't think those wheels are going to work. XLR bolt pattern is 5x120.65mm. The bolt pattern difference may seem small, but even if you do get it to work for your vehicle - it adds undue stress on the lugs and studs as well as brakes and bearings. More importantly, the offset is half what you need. The XLR offset for 18x8.5 should be +56mm.
My recommendation - start by looking for Corvette C6/Z06 wheels/replacements and buy 2 sets of front wheels. I run 18x8.5 chrome Z06 wheels on all four corners.
Snake Bit Super Chilled Black Raven 2006 Cadillac XLR-V aka Elwood (Jake's brother)
Verified 501rwhp and 486TQ at 6000RPM so far...final goal 575/550
ELWOOD - "Corvette in a Tuxedo ... with a Jet Pack"
2013 St Louis Region SCCA Solo SSM Class Champion
Texas Mile Record Holder: Street Legal XLR @ 159.5MPH
ECTA LSR Record Holder: 4.2-5.0L Blown Gas Modified Sports Car