Yeah the 156fmi compared to 1p56fmi is basically a copy of a genuine lifan motor, these motor can at times have odd sized pistons and usually always have cheaper made casings with some strengthening points in the cases non existent resulting in a weaker engine structure, you can buy the really cheap atvs and bikes and normally you will see the engine code as 152fmi as apposed to a lifan 110 1p52fmi same as 154fmi compared to a lifan 1p52fmi, this is why these products can be sold dirt cheap as they are nasty lil engines at times.
If the engine is going into a genuine thumpstar than id be checking the fork travel and doing some measurements to make sure the head on the engine will not connect the front tyre of compression, but if it by chance is the NEW tdr full china so called genuine thumpstar then they have the common pitpro, atomic and so on frame setup and this engine will bolt straight in without any measurements on fork compression.
If you do you will love the 160ho as they rip hard for a stock motor and love limiter bashing.