Then the timing marks will be blocked by the lower hose.
I would use the 273 cover, cast iron water pump, and the 318 vibration damper.
Find TDC and then mark the damper for the mark on the old timing chain cover with white out or white or silver paint. It will make tuning it up easier.
Just keep the balancer from the 318 and then use the old 273 stuff on it...