As long as the bushings are the same size as the 6 cyl ones and don't bind there is no problem. The springs may or may not be the same tension as your originals and that will alter the rate of advance. Weaker ones will let the mechanical advance quicker and stronger one slow down the rate. This is relative to having the same weight and shape advance weights. The cut of the weights limits the total amount of advance and some weights also contribute to how quickly advance occurs by being heavier or lighter than others. It's a centrifugal force thing.
Hard to know exactly what springs you had or have now so there is not a solid answer to your question. If you can find someone who still has a distributer machine they can check the distrib and tell you what it is doing. You can also check the advance rate and the rpm it occurs at with a timing light if you have a clear understanding of what you are looking for. Not as precise as on a distrib machine but close enough generally for a daily driver street engine. Motors Manuals gave full distrib mechanincal and vacuum advance specs. Find one that covers your year engine.
