Yours is the odd ball then, as the ones I've owned were the same. The only difference between my 39A, M and TDS were barrel length plus lever and stock shape
When I called Marlin, they told me the universal part # is 202131 and they are out of that item, maybe in stock in a month or so. But a Weaver #90 will not fit due to the hole spacings.
I'm pretty sure I have an extra one. I have a weaver base on my 39A and for some reason I seem to have two bases. I think. If you get desperate, I'll go digging in the parts bin.
One more thought... how old is the 39M? Could the holes have been added after market?
I have my Dad's 39A (50s era) and it did not come drilled/tapped for a top base... my oldest brother "fixed" that when he was in machine shop classes in college... I'm not really sure what base he used but it's not a #90.
I bought my 39M in the 60's and the Weaver base fit fine. BTW, this is by far my favorite rifle. It has harvested a truck load of squirrels, a few rabbits and a couple of unlucky raccoons. Keep yer powder dry........Robin