The 2 groove input sag four speed has a 3:11 first gear. So with a 3.08 rear gear you are at an effective first gear ratio of 9.57. For a cruiser, this will work but I think you need a bit more gear. With a low power 235, you need gear multiplication to get going from a stop. So for example in the 57 cars with three speed stick transmission, they had a first gear of 2:94 or thereabouts and a rear gear of 3:55 for an effective first gear ratio of 10.43. Trucks had steeper gears because they needed the gear multiplication to get going with a heavy load. Once you are in top gear in a four speed or three speed, you are at 1:1. I would want more rear gear (numerically higher) if it were me. For a couple of reasons, I think 3:08 are too low and lug these motors. Lugging the motor is really hard on crankshafts. So if 3.20s are available, you would be at 9.95 which is a little better in the get going from a stop department and is not a giant increase in rpm at cruising speed. On the other hand, I think 3:55s are a terrific all around rear gear ratio and would put you at 11.04 effective first gear. That's is pretty good and don't let anyone tell you that is a granny gear because I can assure you from personal experience, its not.
As for the sag itself, reasonable in cost to purchase, and they are generally not beat to death like a Muncie is. I bought one that I ran for a few years for like 250. Decent rebuild kits are in the 120 range (you can find them cheaper but the synchro's are total junk). The biggest issue is the shift forks. They wear out. One of the forks is common to the three and four speed Saginaw, the other is strictly four speed. So one is easy to get new, the other a little harder. I think I was another hundred in new forks. Rebuilt it in the basement "laa Boor Atory" and ran perfect first time out. So I had $500 in parts, transmission core, gear oil, sealers, paint and degreaser. Pretty good $$ for a four speed. In fact my son is now going to use it behind a 6 in a 57 car he is rebuilding.
