Had a 81 CM400 (same engine) years ago with 80-90k miles on it that sat for 3 years in my garage untouched with no storage prep, just parked it.
Tried to start it one day and no go and after grinding away for a while a neighbor came over with a can of sarter fluid and the bike started to run and would keep running on the starter fluid. Shut it down and opened the carb bowl drain plugs and some white molasses like stuff oozed out. So we drained the gas tank and refilled it with fresh gas, opened the carb drain plugs and let it flow until the jelled gasoline was flushed out, rode it a short time around the parking lot and put it back in the garage and it became my winter bike (JAN, FEB, MAR approx) for the next 4 years sitting in the garage for about 9 months out of the year. Never touched the carbs except to drain them on that bike and it still ran as good as it always did.
You didn't mention how long your CB450 sat unused after the starter failed. Not saying not to pull and clean carbs if they need it but I don't until I'm sure they do. You seem to have spark so check compression next. Finger over plug hole, crank, and pop would be enough for me to see if it's going to run if you don't have a guage handy.