Long time lurker, first time poster, and a clydesdale at 6'5" 210 pounds who rides more than posts on forums...but this one finally made me register to hopefully help fellow clyde looking for a bike in LA. I have an inseam that is almost 37 inches long. I ride 60 cm frames and can ride a 61 or 59 depending on actual measurement used for frame sizing. A 120 stem and a some seat post showing on a 60 cm frame should work for you. No need to buy a hard to find used big frame - if they even make 64 or 65 or 66 cm frames back then. Now a days lucky to see 63 in a road bike and unless you are a mega tall clyde it may be a too huge frame for you. If you can locate a 60 try it out if possible but even that can be a slim market since most riders are frustrated horse jockeys or just climbing monkeys.

Of course, crank length may determine seat post capability with the shorter crank arm needing a higher seat post. I ride 195 cranks and obviously can lower the seat post for proper seat height and fit. If you have long arms you may need a bigger frame or longer top tube for comfort but a 130 stem can help in this regard if you can find an older used bike as desired with some part swap choices.

Good luck in your search but don't limit yourself to huge frames when a 59 to 61 may do the trick.