All of my Marlin LAs came from the factory drilled and tapped for a receiver sight. I understand that this is no longer the case.
Williams has a version of their "Guide" model that uses the rear two scope mount holes. It's not as sophisticated a design as the FP (lacks micrometer adjustments), but is just as practical and a good deal less expensive to boot. It can be had with a Firesight front of the correct height as a set for about $35-40 from several sources. Quick and easy DIY installation.
Another advantage, again MO, is that the traditional side mounted models quite often do not require that the front sight be replaced in order to be zeroed. IME, both the Williams FP/5D and Lyman 66 have more than enough adjustment to be used with the factory front sights on Marlin LAs.
I believe that Marlin quit providing the means to install a traditional receiver sight as a cost cutting measure, which I can understand given the economic realities we all have to cope with these days. I understand it; I don't have to like it.
If your 336 is a relatively older model, there's no problem. On the latest ones it would require that two holes be drilled and tapped. Around here 'smiths charge about $15-20 per hole for the job. Worth the cost, IMO, for the advantages a traditional receiver sight has over most of the top-mounted designs in terms of relative susceptability to damage, range of adjustment and the ability to be dismounted for scope use and replaced without loss of zero. YMMV.
FWIW, when my aging eyes needed the assistance of fiber optics to regain good definition in and fast acquisition of my sight picture I used the same height blade as the stock one. In every case only very minor adjustments were necessary to rezero.
