8 MHz SPI transmission layout
This answer (Are termination resistors needed for UART, I2C and SPI?) basically tells you that a 50 MHz SPI is probably good for >7 cm tracks. All you have to do is keep clock and data roughly of equal length. Uni-directional SPI is quite forgiving due to the dual nature of clocking data out on one edge then clocking it back in on the other.

At 8 MHz the period is 125 ns and the time given for data to settle (following it changing on a clock edge) is therefore 62 ns. You would have to make data and SCL line lengths massively different to get anywhere near 60 nano seconds in delay.

This answer only applies to sending data out from a master - another greater problem arises when clocking data back in from a slave - this determines the maximum length of track/wire ulitimately but if you are only sending data from master to slave then no problem.