Aligning many takes to grid in project not originally set to tempo

Hi I need some help!
A guitarist sent me a single project of several songs NOT snapped to grid. The guitar parts are in many takes and overlapping segments which he played to an audio drum track which is also supplied with the project. I need to comp and edit the guitar parts into solid takes. Unfortunately if I start applying a tempo track to align the songs to grid for easy editing, it jumbles the takes. I need to have the tempo grid to copy/paste his takes since some songs he only played each part once. How can I do this?
Thank you.

Well if anyone else has ran into this so far this is the best I have come up with…
Comp all the parts as best you can, make any simple edits and apply all your crossfades.
Then bounce all the comped tracks into one long piece of audio. Cut everything in an at the beginning to a matching single time stamp on the existing grid. Now build your tempo track. Then go back through and cut up the bounced audio for each individual song and align to the new grid. Now you can duplicate parts and make and fine detail edits in timing.
If anyone knows a better way to do this I would love to hear it.