U can do a SPA for 600k on the transfer.. then finance it with another bank for 50k..
So your bank will pay off your uncle 30k, and will give your uncle extra 20k in which u can ask lawyer to take it out for you to settle all the transfer costing.

So u will get the property transfer to you on paper of 600k, and u hutang bank 50k, and your uncle dont hutang anything.

Future u sell 650k also no issue..

1. The 550k is not an issue. The bank got to enter into a property with value 600k and charge it for 50k loan.. if you default, they can lelong it and get back with ease... usually no issue. Infact many land and properties are collateralized on 70% and below for quick cash.
Your case is only less than 10%

2. That you will have to refer to lawyer on current rpgt rules. Since he did not utilize it before, he can use once in a lifetime free rpgt. So technically is foc

For my case, the latest RPGT rules is 0% if sold 6th year onwards. So not applicable.