Hmm. Not sure that I agree with your 4-H board.
In the wrong hands, crimping with Burdizzos may not be reliable - but some folks can't count to 'two' and screw up banding, too. I've castrated calves of all sizes with the Burdizzo emasculatome, almost exclusively, for nearly 40 years; done correctly it is very effective. Can think of TWO animals that I 'missed' one nut one - one of my own, one belonging to a client(when I was still in practice); much easier to 'miss' one on little calves than on the bigger ones - you KNOW when you've got that great big spermatic cord in the right place to effectively .
Did have one batch of my own calves that I crimped, nearly 30 years ago, and for some reason - probably because I looked at them too soon - I got the feeling that I'd done it wrong, and attempted to cut them, several weeks later. What a mess! Scar tissue/adhesions galore - and the testicles were atrophying; I mucked around with 2, maybe 3 of them, and decided that it had indeed worked as it should, and left the remainder of them alone.
If you've got to comply with your 4-H group's misguided requirements, I'd probably opt for banding, provided you have enough time for the scrotum to fall off before show time - but, as recommended, make sure he's up to date on tetanus vaccination. Do NOT just give a dose of tetanus toxoid at the time of banding and hope that he'll respond faster than the C.tetani can begin making toxin.
Any chance the veterinarian who performed the initial procedure would have any influence on the 4-H board? Seems a shame to put this calf through an additional stressfull and painful procedure just because someone mistakenly 'thinks' that it's an unreliable method.