*twickn29zero:
The car I bought already had the engine with it (indicated on the CR) so I have no idea on the paperwork.

A Honda specialist shop nearest to Paranaque will be Hongly along Sucat Road. They're a bit pricey than those in Evangelista like PSI and Initial D, where a D15B complete package and installation may cost around P45,000.00.

However, to answer one of your initial questions, yes it will match your PH16A transmission.

I don't know why and how your "mechanic" said the engine is retiring. In most cases, it can be overhauled or rebuilt (rebuilding may cost more than engine swaps though). The good part in overhauling is that you don't have to mind paperworks, which I heard could be such a hassle, not to mention costly.

Want D15B power? Get a D15B cylinder head + P08 intake manifold + P08 ECU. They bolt straight on to your PH16A block (given it can still hold the compression from that high-revving head).