Looks like threads/tenon was cut off the barrel to me. The distance from the action to the back sight is shorter than stock. A M70 barrel has a bolt/slot cut for the extractor, so it'd have to go anyway. The thread diameter on a M70 is 1 inch is slightly smaller than the 98 1.1inch, but I'm not sure there is enough left to turn and re-thread. The notch would have to go anyway. I'm guessing the M70 barrel was installed to save some money. Pretty cheap to chop, thread and rechamber vs a new barrel. I like Frankenstein rifles!