Correction, it will cost considerably more to find out it won’t work than just the cost of the block, like time (is money) and possibly non re usable parts to assembly and test it plus another failure could do greater damage.
Just my opinion but I think a new block would put your mind at ease and cost less. As far as welding on the block, you can still do that and make a pretty good determination by NDE of the quality of the repair.
Bare in mind the heat sink qualities of Aluminum and the effect it may have on all the very high precision configuration of the block.