I bought kelfords beehive springs, larger tappets, their valves and cams. Put these in my car and it didn't make a huge difference to power levels around extra 10wkw. I did have reprofiled cams before though through Franklin so didn't expect too much.
Getting the larger tappets In which hold the springs in on the valves is a bloody hard job, they are around 50% bigger than th OEM part. I've built my own heads a number of times now and these are way harder to assemble but are worth it as they are far better at holding the valve, spring etc in place, reccomend them.
I line bored my crank too and has extra dowels In there to help hold it together.