the 222 would need a massive buff to make it a threat to the stuarts/t70. The stuart have nearly 2x the hp for starter.
normally this would be a job for puma, but it's a doctrine unit. Unless Relic make the puma a default unit....
Put the 221 in T1 with no up-gunning. If the MG is already T0 it fills that slot in T1. Give it Vet 1 capture territory powaz like T34 / T70. Now you have a light scout / harassment vehicle that is still very vulnerable, a beefed-up CoH1 US jeep.
Put the Puma in T2 with a 20mm cannon with the option for upgrade to 50mm.
Job done. Tweak fuel to make both a balanced but not risk-free proposition. Soviets have guards / AT nades and T70s to deal with both.