Upgrades for Cougar Laydown

[Randall34]

I am about to buy my son and I a pair of Cougar Laydowns and build them together.
As we are buying kits the rollers will be standard.
I am always a sucker for hop-ups and upgrades, but as I now have to buy two of everything I wanted to get some advice from seasoned LD owners.
We race on astro outside, mainly dry (we have other cars for wet conditions).

Which upgrades are 'must haves' (ie alloy parts, brass weights, springs and pistons etc)?

Which are 'could gets' if you fancy it.?

Thanks in advance.

Neil