Adding 76 or easy8 would be over the top if they were some really good tanks, but they are roughly at the level of p4 (76 = ost p4, easy8 = okw p4). From what we have seen so far balance team has no intention on improving usf units beyond small "buffs" like the calliope insignificant change so both sherman variants will probably stay the same. Easy8 + calliope doesnt offer anything that axis faction cant deal with (especialy with new broken commanders of their own) even with calliope getting its gun fixed.
How i see calliope with working gun is having it only to shoot HE sheels (like sherman) so it cant defend itself against armor. There should be switch option (again, like sherman) between HE shells and rocket launcher with something like 8 seconds delay before you can use one of them. Then you could leave the terrible calliope barrage as it is since it could be used on frontlines too. And now calliopes good survivability would matter.
76 and easy8 are both good tanks and better (especially than ost p4, basic Sherman is equal to it). And the balance team has improved USF enough already.