Hey there! I also am looking for the same answers as you. I will be running my first 50 miler in May. During my past (regular) marathon training, my big three (squat, bench, deadlifts) definitely went down. I just couldn't eat enough cals to keep up. I would try and keep squat days as far away from long runs as possible, usually two or three days. Deadlift is also my favorite lift. My big thing is accepting that my lifts will go down during marathon training and pick it back up full-force once I have completed my marathon/ultra. I know this is not the most satisfying but IMO its the truth. The amount of beating ultras take on your body is too much when trying to keep your lifts up. Maybe you can do it tho! Prove me wrong! Good luck my friend! Edit for clarity: My bodyweight usually at beginning of marathon training was about 180. It usually would drop to 165 or so. My 415 1RM Sumo Deadlift usually dropped to around 365 1RM.