P.S Defo a FCD type device and not an ESL board.
1st time I have seen an FCD/Superchip mounted like that too, although I have seen a few variations.
As you mentioned, it's a 1C is from a WRX Wagon of v.early vintage.
Standard boost on the TD04 would of been 10.4psi dropping to a mere 6.8psi at the top end.
The ESL solders to the 28 pin DIL postion that is just under the black box in your picture. There are 2 generations of ESL, the early chip-able variant that retailed for about £195 and can be bought for around £60-£100 2nd hand. And the Version 2 live mappable that were £295+VAT.
The J1 brown resitor (on the right of the vertical board in your picture) would also be cut or missing if it were running a map from the spare 28-pin DIL location.
Piccie of the Version 2 ESL board which is same fit but different component layout is on
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