I would NOT alter that rifle for a Mossberg scope.  They are very dim, cheap, and low power.  They are not from the era either.  I've had several and mounting a paper towel tube would be about as good. It's like taking a pre-64 Winchester Model 70 and putting a 1970s Tasco 4X on it.  Don't.  If you can get a GOOD early scope, like a Fecker or Targetspot, then I suppose that's ok.

I replaced the Crosshairs on a Mossberg scope on a Mossberg heavy barrel rimfire bolt rifle for my cousin. The scope itself was remarkably clear and would work very well for your 100 yard personal use as you have just described. I don't recall the power I thought it was 4X from memory but I could also be wrong its been at least fifteen years ago now.

Got the rifle on Friday, a bit disappointed, bluing to bbl and action faded, bbl as new internally, also got 53 fired cases, so in my opinion if this even is all it has fired I wouldn't call it "mint", you win some you lose some !!
Interestingly the cases have a head stamp that is new to me, have " 25-20SS", what looks like an eagle with outstretched wings, and a "proof" mark I cannot read. Have a friend collecting the balance of the live ammo that was included in the deal so may have original packet, which will let me identify the maker. Used cases, have all been annealed. The saga continues!