kingkongkecik,
Not all banks offer the same loan deal as Public Bank. Some banks may offer a better loan deal. U may wanna check with banks like EON, Hong Leong & etc. About the 100% loan for second hand car, i really have no idea. But i do know that some used car dealer may be able to do so with some fee.
As for the engine mods, my priority when i mod the engine was, firstly reliability of the engine as it is my daily transport. Secondly is the ride comfort, such as engine idling & thirdly is the fuel consumption.
Hope the above helps.