SV Header Primary and Tail Pipe Length

We have a Lola SV (air-cooled) in the shop for new headers:

Any one have any idea how long to make the primaries and tail pipe on a 2L FSV type 4 engine?
Using 1-5/8" tube, 2-1/2" tail pipe material.

(I know that it depends somewhat on the engine build, looking for basics here.)

As it was the old primaries had varying lengths from about 26 to 28-1/2". Seems short to me.

I've built many FV systems but not air cooled FSV.

Any thoughts are appreciated.