I own a 64 impala SS. Had a 327 with a 2 speed powerglide. I’m going to a big block 396. Was curious what transmission is better, the th400 or 700r4. I’m favoring the 700r4. I’m only going to cruise it on weekends, if that. Would like to know if anyone has installed one in a 64? How tough was it? Any insight would be appreciated.