I know most won’t agree with me but I’d say bite the bullet and build a set of headers. Every time I’ve replaced manifolds with headers I’ve been happier with the way the engine runs. We did some testing a long time ago on back pressure in the system with headers vs manifolds and the backpressure drops a bunch (with no other changes) and a corresponding jump in hp followed at the same boost level. That’s what I wish I knew in the beginning.