I wouldn't try to copy at all. As the designs you have mentioned have highlighted, the advantage Clan technology has over the Inner Sphere is too great to try and copy a design in most cases. As you would have to sacrifice something to attempt to come close, such as ammunition, armour, speed, weight, etc.
It is easier to try and copy Clan designs that make heavy use of LBX autocannons, as they do not have as great an advantage in this field, usually only saving one ton of weight compared to the Inner Sphere models. And trying to copy designs that make heavy use of missiles is downright impossible due to the Clan versions weighing half as much.
The Rakshasa is the best example of why not to copy a Clan design. Pretty much everyone designs that it is a poor copy of the Mad Cat, (Though to be fair not as much as a lemon as most make it out. Due to being compared to a superb Clan design) but the one variant that just gave up on trying to copy the Mad Cat tends to be seen as a rather strong design.
It is however a interesting design challenge though to try and design something that is close to the capabillity of some Clan designs using the inferior Inner Sphere technology.
The Rakasha is a pet project of mine, similar to the zeus where its not bad as it is, but theres more there, but its a challenge to find that point where the mech is better then the original, but has not strayed to far from the original as to be a unique design.
The Raka is no match for a madcat. The madcat's success with the fan base is really due to it being a great platform to display the differences in clan tech vs IS. 2xLRM20s? Better lasers in large and medium sizes? The only other thing it doesn't display is the difference in gauss rifle tonnage, but even then it does not have as big an advantage as clan LRms with tonnage and min range advantages.
The best way to mimic a madcat using a rakasha would be to use MRMs instead of LRMs.
***edit***
this got me to poke at the design again, instead of opting for mrms I decided to do something that could even the score a bit.
I dropped the speed by 1, I know its supposed to be as close to as a madcat as possible but it did free up tonnage that it really needs. You can't match clan gear by going for the same speed, overall tonnage, and damage output, its just not possible no matter what because people give the clanners their own version of everything the IS gets save the C3.
i upped the armor by .5, not huge.
opted for 6x LRM5s which is going to get 18 points of the madcat's 24 points of lrm damage a turn.
dropped the 2xERLLs for 3x light ppcs and an LBX5 with 1ton in cluster and slugs, giving me 20 points of damage to match the madcat's ERLL's 20 damage.
Went with 4xMLs giving me 20 damage for the madcat's 2ERML+MPL's 21 points of damage.
When it comes to ammo the LRMs on my Rakasha gets 8 turns of firing vs the 6 for the madcat.
If you can get the madcat to deplete it's lrm ammo before getting into short range it will have a potential for 41 damage(erml,mlp,2xerll) while the rak can put out 40 damage (20 from MLs, 15 from LPPCs, and 5 from LBX5) with just a slight bit of overheat.
It can't match the range brackets of the madcat, but it looks like it would have a change against a madcat though.