If what I highlighted in bold is accurate, you will need 8D in the leather LWBs (tobacco waxed?) and 8.5D in the Perf Cap Toe color 8 (shell) boots. J Crew doesn't offer anything other than D width in their Alden make-ups, so this rec should be your best option. Good luck! (BTW, I have both of these pairs in the same size but the LWBs feel much more roomy [wider] than the boots.)
This is my experience as well. I wear an 8.5D in the LWBs but found 8.5D in the JCrew cap toe boot to be too tight. Going up to 9D in the JCrew is perfect for me. This is consistent with the other Alden cap toe boots I have, they seem tighter generally than the LWBs so I get the cap toe boots up .5 size.
To make it more interesting, I have found that with a leather sole corodovan wingtip boot 8.5D is comfortable. But when I tried a commando sole corodovan wingtip boot 8.5D was too tight.