Hello All - My AMAL carb body is beyond repair.  I’m looking for alternative new low cost carb options please. 

I believe an OKO works well. Check out Mid Atlantic Trials website, they have tested and tuned these for best results with the 247, and theirs are the genuine OKOs not the useless Chinese copies. The price exported  to you in the UK isn't bad compared with a new Amal.

Mikuni is another good option,   

and if low-cost is important, you can buy many used Mikuni's  that are still serviceable 

- unlike Amal , where 99% of used ones will be completely worn-out due to the rubbish metal they are made from 

Had the same problem as you with my OSSA 250 MAR about 5 years ago, got a good used Mikuni & a selection of jets ,

after some experimenting found jetting that suited the bike , and have had no carb problems for 5 years 

Search for Motocarb they supply Mikuni carbs for all sorts of bikes