Tasco used to sell 2 different one-piece bases for the Savage 99 that allowed for the use of Weaver-style rings.
The BM-99 is a steel base that has a nicely polished blued finish.
The 841 is an alloy base that has a matte dark gray, not quite black, finish.
The BM-99 base is aesthetically more pleasing, more in sync with a blued and walnut rifles, and is (IMO) the best looking base for use with Weaver-style rings on a 99.
These Tasco bases sit a little lower than any other bases that I've installed on a Savage 99. They show up on eBay from time to time.
I received a message from someone who saw a Tasco 841 base on eBay with a label indicating that the 841 base fit Savage 110 series rifles. This person accused me of putting out incorrect information. So, I bought the 841 bases that he wrote to me about to see if they had been mismarked or it Tasco had changed their model numbering protocol. The packages do indicate that they are for Savage 110, CIL 950, and Revelation 250 rifles, but the bases are exactly the same as the 841s that I have installed on a dozen or so 99s that were factory d&t. Over the years, Tasco changed the packaging for the 841 bases from blue, to yellow, and then to gray and red. All of the 841s that I've seen in the blue packaging have indicated that they were for the Savage 99, 1895. CIL 900, and Anschutz 153.
I don't know how many of these mismarked Tasco bases are out there, but I just got 2 of them off the market.
PS The blue packaged Tasco bases that I have are base and ring sets, while the yellow packaged Tascos are only the base.