There are no known generalized repunit primes in base 574, it is only a cofactor of a generalized repunit number in base 574.
For the smallest generalized repunit prime with at least 3 1s in bases 2<=b<=1024, some largest primes were found, the top 10 (probable) primes are: (sorted by exponent)
(152^270217-1)/151
(18^25667-1)/17
(333^9743-1)/332
(536^6653-1)/535
(922^5987-1)/921
(469^5987-1)/468
(702^5897-1)/701
(1012^5749-1)/1011
(683^5483-1)/682
(230^5333-1)/229
There are no known generalized repunit prime with at least 3 1s in bases 184, 185, 200, 210, 269, 281, 306, 311, 326, 331, 371, 380, 384, 385, 391, 394, 396, 452, 465, 485, 487, 511, 522, 541, 570, 574, 598, 601, 629, 631, 632, 636, 640, 649, 670, 684, 691, 693, 711, 713, 731, 752, 759, 771, 795, 820, 861, 866, 872, 881, 907, 932, 938, 948, 951, 956, 963, 996, 1005, 1015. (less than 1024, perfect powers excluded, since if the base is a perfect power, then generalized repunits can be factored algebraically)

To be completed...