It is not hard to upgrade too obd1 because the system is technically already OBD1 setup already but is rewired properly with an OBD0 to OBD1 jumper harness.
Here is HAmotorsports.com - 88-91 Honda Prelude OBD0-OBD1 jumper harness
Do not go FMU as it will blow up your low boost setup in a short time. This is why so many have blown their budget builds in weeks and months and sometimes on a first drive.
Do it right the first time.
As for turbo manifolds only one person makes them on demand and he used to be part of this community and then moved onto the NSX crowd.
Here is his site: https://www.foundry3studios.com/product/b20a-t3-manifold
- Basic B20A Log manifold, same fitment as the ludespeed only better designed for more flow.
- Accommodates 600whp without loss due to large runner diameter, enables fast spool thanks to short runner length.
- Available in polished, standard, or ceramic coated finish. Stainless flange option as well.
3 week wait for assembly.