Is there any difference in using the 1275 Float Bowl that have a different casting?

I snapped a screw on a bowl.

I was able to find another one but it is slightly different where the plastic/rubber piece slips into to the groves.
In the next picture, the top bowl is my replacement. The only difference that I can determine is the star type castings.
Should the one I found interchange?

I can't imagine it would be a problem - try it and see.

The bolt looks like it will drill out easily though. and just a reminder that if you take apart and put back together an SU carb enough times, you will eventually have two carbs. :grin:

I may try to drill and use an extraction bit (easy out?). I had some luck on my exhaust manifold

I will not use and do not own easy-outs. They typically break and make the situation worse. However, it's your car, do as you wish.

Consider this. The screw you are trying to remove broke because its threads are really stuck to the float bowl. To use an easy-out you are drilling a small hole down the center of that stuck bolt and trying to use a left-hand hardened extractor to somehow break free what could not be broken free when the bolt was in one piece. Instead the brittle easy-out is likely to break off in the hole. The only time easy-outs seem to work is when you are able to drill out just enough of the center of the bolt to release stress on it... yet have enough remaining bolt that the extractor cannot cause the broken bolt to expand outward. God forbid you break an easy-out. Once those are broken off in a broken bolt you are left with carbide cutters as your solution... unless you happen to work with a shop that has an EDM machine.

My advise, just carefully drill the bolt out using progressively larger bits until you can pick the remnants out. If you happen to have a set of left-hand drill bits... that's all the better. If you need to re-tap the hole you can use a readily available 10-24 tap.

Doug any comment on using the other bowl?

Try the other bowl with the rubber spacer washer. If you can position the replacement bowl so it is as level as your other carb's float chamber you will be fine using the donor.