L. caeruleus are incredibly difficult to sex accurately until they're almost adults. You may think you have a group of males only to find one holding one day. If you definitely want all males, you'll have to buy adults and vent them.
I had 3 yellow labs in my 55g. tank for about a year. I finally decided that they were all male. Out of the blue 2 of them stated picking on the one really bad and I had to remove the one that was being picked on.
Tank size 6 ft x 2 ft x 2 ft (180 gal)
There will be other adult fish in the tank too but only one of each species or similar look.
I plan to put the labs in a 55 gallon until I can make sure I can pick out males. If they breed in the 55, it won't bother me since it doesn't have overflows. I'm just afraid that if I put a group of males in the 180 gal, they might not get along. Its a hard tank to remove fish from.
The tank is certainly an ideal size for it. All I can say is it might work, you just never know how an unconventional setup will go. Even conventional setups are never guaranteed to work, but the odds are usually in your favour. I've kept multiple male L. caeruleus together in various setups without incident, but there was always a female or two.