Measure the center-to-center distance between the action screws. If it's 7 7/8", it's a standard length. If it's 7 5/8", it's intermediate. If it's longer than either of those, it may have been lengthened (unlikely).
ETA: The trigger guard looks like it's off a VZ-24 with the cross-hole in the front of the loop. I don't think it's totally unique to the VZ-24, but I've never seen an intermediate length action with that particular feature. If it is a VZ, it's a standard length action and one of the better ones at that.
ETA again: If you're looking to get rid of the stock that's on there, and it's not damaged, I'm interested. I have a Spanish M44 that needs one.
Matt