Nothing wrong with wanting one of Benji's bikes.
Just for reference, I have a cb500K1 that has a 16x3 drop center Harley rim laced up to the factory hub.
I am running a Kenda Challenger 130/90/16 tire. It is 5 5/16" wide and 25" tall. I have just over 3/4"
from max tire width to either swingarm inside edge. I have an aftermarket chainguard that has less
interference and the chain is 3/8" from the tire. The brake arm has a mild bend to it for extra clearance.
I have nearly 10,000 miles on this combination(with a 100 series challenger front tire on the factory front
rim) and have had no issues at all. I am not, however, a good source of potential handling issues as I have
never pushed the bike very hard in the cornering department.
FWIW, it appear that the swingarm can handle a 150 series tire or more spacewise, but the chain will
require an offset for reasonable clearance. I can't imagine a 130 series tire on a 2.5-3" inner bead width
18" rim would cause any challenging issues clearance wise. Obviously a 130 series tire on the factory 1.85"
rim would be inadvisable.
George