just removed small block out of my 69..installing big block,,checked spring hieght before removal and after added 100lb weights in my engine compartment.only sunk 3/4 of inch after couple of days..will my springs be ok with big block install or should i change to big block springs,,heard they make car sit to high in the front,,??

If the springs are relatively new you can go with them if you are on a budget, but if they are worn I would replace them with BB springs. They may look ok as far as ride height but do not have the stiffness needed to keep the front end from bottoming out over rough roads or roads with dips. I have done a lot of SB to BB conversions and I personally would go with the BB springs.

I left my 6 cylinder springs in when I did my '64 BB conversion 15+ years ago. It's low but has excellent weight transfer.

thanks guys,ill take advice into consideration,appreciatte it...

The extra weight of the big block will sag the springs a lot over time. If you want to keep the ride height low,buy some BB lowering springs from someone like Coil Spring Specialties.