Given the condition of that backplate I certainly would. For a couple reasons:
a) A chuck that size with only two pins just isn't safe...
b) You run the risk of damaging the spindle of your lathe.
Seconded, plus-plus.
No "risk" to it. You
WILL damage the spindle. Chuck as heavy as that ain't no junior birdman's low-stress near-as-dammit right ON center 5C collet adapter.
Only thing as makes any sense atall was adapting that chuck to use as an indexer, a positioner on a bench fixture, or a low-stress grinding or polishing operation - even welding - but in any case OFF the lathe spindle altogether.
Such needs do exist, so it might have "seemed like a good idea at the time" to some prior Pilgrim who ALSO had a better chuck with all its "fingers" for use on the lathe and "the usual" work, this one simply available to re-purpose on-the-cheap, quick, dirty, and near-zero cost to address some other challenge effectively. No sin, that.
Most of us do much the same when we have those needs. WTF ELSE can one do with a mere THREE-Jaw chuck as ignored the "ban" and sneaked under the door by accident? Guess I shall have to buy a welder, now?
But it was whatever it was - stud mounting holes filled-in, not "temporarily borrowed"' a dead-giveaway.
I'd look it over closely, VERY, before spending a dime fitting a new back - which I always have one or more stashed, (D1-3 here) just in case.
Chuck may have been crashed, worn, or otherwise found wanting on strength, max RPM, or, or .. wotever...to have been sent-off to secondary duty in the first place.
3CW