Pre-Improvement Hit/Initial Hit from the U6 arc was slightly weaker than U6 arc SSB Goku.
Base Goku Black after training to sync up with his body was somewhat weaker than Beginning of FT Arc SSB Vegeta, though he was able to take a punch barrage from him and land a solid kick on him. There's not much pointing to there being big gains for Goku and Vegeta's SSB forms inbetween the U6 Arc and FT Arc however.
So I would place these two versions of the characters around the same level in power.
Restrictions: No improvement or zenkai. Fight is entirely H2H (hand to hand combat). So no special abilities or energy attacks for either side.