Maybe you can find a butt end that will fit the holes where the clamshell goes.
Or, you can make a plate that fits the two holes where the strainer fits with two more to mount a butt to. There's a thread somewhere that describes it better.
Clamshell butt ends come up way more often than the strainer side. You will find one in time, but until then the retro-plate idea has worked for many in your situation before.
Ha !!.... I just found a correspondence with Bobby at Drum Farm... here's the text......
This is for a 3-point strainer, just adapt it to your situation,..... you'll see.
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Just a quick note to mention making an adapter plate to fit any other strainer to any drum.
Get a thin adapter plate to fit between the two.
thin Aluminum works great.
Drill 3 holes to match the drum's pattern,
and drill holes to match the throw off you are using.
Drill the adapter plate that is.
Then countersink each set of holes from opposing sides.
Then, purchase V headed machine bolts to fit the holes and length you need.
Buy the nuts and washers to fit.
Bolt plate to drum while the other screws point out and become mounting posts.
Voila.
Bobby
Easy, Easy, Steak and Cheesy