The largest ive seen in person were not on a river. We owned property on the Brazos for many yrs and Ive seen 6-7' gar there. But a bigger lake like RC has monsters Larger than 7'. Most have already scattered again. On lakes this makes them difficult to find. Contrary to popular belief ive found them all over our area. They r found more so in rivers such as the trinity & brazos however. When they gather in the Spring & Fall they can be targeted on lakes more easily. Christian has a good method for catching them IMO. Use a whole gizzard shad a good chunk of carp or a whole perch n Give them plenty of time to get the bait down or u will lose more than u catch. It takes patience, a strong & VERY Sharp hook, planning & other right tackle. The really big ones school up in the fall and arnt landed on conventional tackle.
Lusca knows how to land them and will tell u he's not always successful. You got to really want to catch a big one IMO.