I am in need of a set of headers for an '87 with a 395W. The engine has
400HP/500 FT-LBS TQ.

The problem is I can only find headers with 1 1/2" primaries I need 1 3/4" as that is what my heads are flowed with.

I have looked everything where, about ready to have someone make them

 

Bassani makes an equal length set of shorties for a lightning (5.8) with 1 and 5/8 primaries

Part# 58150LC Bassani Exhaust - Bassani.com

 

I have seen those and they should work, I was really hoping someone would be able to come up with some 1 3/4" longtubes!

I never would thought all the aftermarket would be so small

 

Most aftermarket are designed for some readily available stock or "relatively standard" aftermarket heads and flow rates. If you get much beyond that, you are left with the predicament you find yourself in.