Scott,
On the front tire sizes , while we have not yet done a 69 in house , I do know of a few customers of ours that have done both a 265 and a 275, and both worked well , without any modifications other than making sure you get the correct backspacing on your wheels.
However , I would suggest you go to the Roadster Shop chassis Vendor section here
https://lateral-g.net/forums/showthread.php4?t=54852
and check out the great chart showing actual real world results of a 245 front tire versus 315s, I think you might find it useful.
No floor mods are necessary for the T56 , you will have to re locate the shifter hole obviously.
While Ride Tech makes a great shock, the shock body, lower mount, and upper spring retainer will not allow it to fit on the front of the SPEC IFS. The base shock is a Strange Single Adjustable and you have the option to upgrade to an Afco Double Adjustable or take it to the top level and do a Penske Double Adjustable or Triple Adjustable remote reservoir shock.
Thanks , and hope this helps answers some of your questions