Measure the plate blocks (in mm), then buy the appropriately-sized Scott/Prinz/Hawid/Showguard mounts. Just about every philatelic retailer will carry some or all of these, like
https://www.ihobb.com/c/STAMP_MOUNTS_HINGES.htmlThis presumes, of course, that the pages of your album are thick enough to support the weight of all these blocks and mounts. My suspicion is that they're too thin, since most of these older albums just assume the owner will use hinges (which would defeat the whole point of you having gotten all of these MNH).