Purchase BOM without subcontracting

I have scenario mainly for capital items in imports where procurement is done as package items in different baskets say a package of instrument items in baskets of flowmeters, control valves,pressure transmitters etc. Each basket will consist of different actual materals. Say a basket of control valve may consist of 1 no control vale 50mm, 10 no control valve 100mm, 50 no control valve 150mm etc

Vendor rate is available against each basket and supply is made in stages. Say we receive 2 no 100mm & 10 no 150mm in 1st consignment. As per agreement & terms payment is also to be released accordingly

It is difficult to do GR without a BOM for identity as per actual material. Also payment of GST on customs duty which is HSN based as per custom bill of entry and each basket may have materials with different HSN code

Subcontracting PO with item category L, although has provision of components, but this cannot be used. In subcontracting the BOM components should be available in vendor stock which after GR gets consumed. Subcontracting is used for jobwork

I am sure such scenario is available in other industries and must have been tackled my experts. Request is for sharing the expertise