I had the same problem, I bought a Romac balancer, they are all steel, SFI certified, and mine measures under 5.875. Mine is part #0206 for an internally balanced SBC. Hope this will be of help. Right around $150.00
Find top dead and build it, if you do not have the equipment I see some adjustable timing pointers for 6” and you may be able to modify it we are only talking a .100” difference