If the properties are essentially the same size since you allocated 50% to the rental, then yes, you would allocate the purchase price and cost basis by 50% as well.
In the long run, this will probably be you best solution in the event that you ever decide to rent both houses.
You would also change the property type from multi unit to single family.
[edited 4/15/19 | 9:54 am PST]
