The 305mm Computar is the lens you would like to use but they are both scarce as hens teeth and when they are found, cost a King's randsom. Next best "wide angle" I believe would be the 355 G Claron. I have seen some in barrel that were not that expensive. I have an extra that has a very modest amount of bloom on the outside edge of the rear element that would very easily clean off if you are interested.
My 12x20 and 8x20 lens selection is 355 G Claron, 450M Nikon, 19" Red Dot, 24" Red Dot, 30" Doctor Germinar, 35" Red Dot and 42" Red Dot. Don't use the 35" or the 42" focal lengths to often (if at all) as they are both heavy and most of the time need secondary tripod support.