What type of aluminium is good to weld yo a lc top end ?

I want to fit a decompressor to the head of my 87 430 because I lost some weight and it's too hard to start now .
Has anyone got anything to say about what grade of alloy would be better or worse to use to make the boss from ?

This place does welding on vintage 2-stroke heads. Touch base with them - they may be able to help:

https://www.2strokeheads.com/index.php/sale

I recall that Tjiebbe Bruin (oops spelling) in Auckland could fit an automatic de-compressor to a Husky. I never spoke to him about it. I was told that he could start his 'customised' auto wearing sandals.
If memory serves me correctly he fitted the de-compressor to the cylinder (probably mid stroke) and a small tube went down to the crank-cases. The de-compressor was normally open and was closed off by the positive crank-case pressure once the engine was running.
Somebody told me that he used a unit off a lawnmower. If he is still in business it might mean shipping the whole engine to him for fitting - or he could give you instructions and you do it yourself.

The decompressor on one of my 430 ae is fitted on a cooling way.
There's a brass part that is screwed on the cylinder. The decompresseor is screwed on this part.
Must have a O ring between the the brass part and the cylinder.
The cooling way has moved on the left.

Well I went with the no welding option because I dont have one .
Through the side of the cylinder would have been preferable but this will work