Ewazix has a good point JE, it might be a good idea to prep just by getting the cash in place for these things. if you change the engine then you may change the weight so need a different poundage in the springs. so might be a better idea to get the cash in place and then once the new engine (3.0 supercharged, V8, V10, merlin spitfire engine ??) is in place get the car corner weighted and decide from there.
maybe you've thought about it already but i would bet that the spring rate for a 2.0 is less than that for a 3.0.
its something i never considered till i built the westy and was told about it.