Any benefit to fitting a velocity stack(s) about midway inside a UNI type of filter?
Dunno about that, but adding 4" intake runners between the filters and carbs made a big difference in the low/mid range on my KH400.
Is this on the bigger VM's of stock 28's?
Not really on bigger aftermarket VM and YES, works good on stock 28's by using a connector ring and stock airbox tubes to the uni.
Chuck