nearly 300 people died 'cause the experiment is impossible (vol 21 says this). Burando recognized it as impossibile. You can transfer partial immortality which lasts for a short span of time.
if shira tried to fit manji's arm he could die if the blood-type is not compatible. So at the very least, he should wait to use the arm WHEN he's facing manji. It would be stupid to try before and die while waiting for manji.
also, in recent chapters he's still got his spikey bone. So, as things stand now, he still hasn't used the arm.