What length riser stem do I need?

[sefton1275gt]

I usual ride a 54cm (effective top tube) with a 12cm regular stem (-6 maybe)?

I have a new (old) bike that has a 58 effective top tube.

However rid like to raise the bars about 4cm

What degree riser stem and how long should it be to achieve the 66cm length I like.

Also, it's a 1" fork steerer. I noticed there are many spacer kits to convert to a 1 1/8... Are these a reliable / durable solution?

Below is my stwm without the top cap

 

[bikeworkshop]

If you're happy on 54tt, it's unlikely you'll like 58. Even if you adjust the reach to be the same, the steering dynamics will be very different.
20mm is perhaps the limit.
Inch quill to 1&1/8,ahead adapters are heavy but effective.

An inch and an eighth stem will look awful on a narrow inch quill steerer tube though.

 

[sefton1275gt]

I plan to tour / bike pack on it so I wasn't overly concerned about the bigger frame size.

It's not currently a quill stem.

 

[bikeworkshop]

If you put your elbow pushing back on the nose of the saddle, you want the bars about an inch away from your fingertips.