Just sidebar for scale. The original Titans were 1/500 not 6mm:1/300 which generally was what Epic is/was. Even with the scale creep that has occurred over the years with the different versions of Epic.
E.g. if you count the original metal Eldar Infantry. You have 3-4 different sizes. [Maybe some Craftworlds Eldar grow larger warriors than others ?] Also even the E40K Orks were a little bigger vs. the original Ork sprues.
Add to that the original SMs including the original metal ones. There is 3 different sizes.
The original Mk.VIs are smaller than the Mk.VIIs. And the original metal SMs are closer to the Mk.VIIs.
So if we can take anything away from GW is that "Epic Scale" is "negotiable" ...
Also the weapons' range differences between 6mm & 8mm would probably not be an issue. In many cases the ranges were a little too short for many 6mm Epic weapons. E.g. In reality most of the Artillery in Epic would be off the board. FA has very, very, very, long ranges. The only way they'd be on the board in situations that we saw in Stalingrad, Berlin, Manila, etc., in WWII. Used at close range in direct fire mode. To blast enemy fortified and occupied structures.
But that comes under the umbrella of model scale vs. real scale vs. game scale, etc., IMO ... But as we see Game scale vs. Real scale vs. Model scale is not really a factor generally in 40K scale games. Titans should not be on the table in that scale. E.g. You wouldn't generally see a large naval vessel on the board in 6mm - 28mm unless you are doing a scenario like the Campbeltown/ St. Nazaire Raid in WWII.
https://en.wikipedia.org/wiki/HMS_Campbeltown_%28I42%29 Just some food for thought ...
But again DWW4U ... NM ...