Hi, I still have YR4SP with red shocks too.
This car could race competitively with current car model, don't worry, you will not at the back as long as the car is completely stable.
Do you know that YR4 cars are lighter than mr4tc sd ?
Shock upgrade ? I'll pick Tamiya TRF.
On Road : Xray NT1 , RX8 , T4 || Mugen Seiki MRX4-R , MTX4 , MTX3 prospec || Tamiya M03 , M04 || Top Racing Sabre FD2
Off Road : Xray XT8 || Hobao Hyper 8
Radio : Futaba 3PKS || KO propo EX-10 eurus