So I did a lot of futzing about for battletech 2300 covering a lot of similar ground for the stuff that would be around for the terran hegemony terran alliance war. More or less and excuse to use interstellar ops and go crazy.
If you do something something similar, you have industrial 'primitive warmechs' which get a few more penalties compared to normal industrial mechs, but they existed long before primitive battlemechs. They are the first thing that gets "free" engine heat sinks, and the medium and small lasers are JUST out of primitive stage. So these early warmechs are great medium laser platforms. You can make a pretty convincing primitive industrial mech archer at 3/5 speed for example.
Vees are all built with support bee rules. This meant I had 3 tiers or 'blocks' for each vee at tech B, tech c, and cutting edge tech D with 1-2 fancy compoments that existed by 2300.
TechB is 1950s cold war stuff, but since I included anything that was tech B, you also get I-os missiles. An i-os lrm5 and i-os srm2 are the missiles of the era, along with rockets. The iOS srm2 with heat seaker ammo in particular makes a fantastic sidewinder stand in on jets.
Tech C is post 2000 stuff. So you can get an engine not powered by gas/ice and can mount higher grade BAR. The armor on a tech C tank is much lighter at BAR6 unlike the tech B super dense stuff representing the 90s and their love of depleted uranium to bolster the 60s era chobam. You also get the autocannon, which may not punch like a rifle in this era of BAR armor, but it has great ammo endurance and most importantly flak ammo. Airpower is super op in the early days as bombs haven't changed much at all, so flak ammo is godly. All primitive aircraft have BAR 1 armor or worse as they dont get normal thresholds until way in the future with bar 10. So a 2 damage ac2 threshholds any aircraft in existence, and the ac5 flak is even better as the cluster on flak is much more consistent at causing threshholds. Flak ammo is also better versus infantry then any other long range gun, so quad flak ac2s can deal with infantry safer then almost anything other then artillery.
Finally, infantry and artillery. The humble autorifle is crazy solid DPS for tech C infantry. Tech B have to make due with rifles and mortars as you would expect 1950 infantry to do. But artillery is king. Thumpers and long tom has stupid high damage for the era... 15 damage when the next best is the heavy rifle at 9. With 5 damage cluster size, heavy armor on tanks can take some hits but everything else gets shredded. So you have a nice balance of tanks with BAR crushing cannons, infantry for dps, and artillery for fire support.
I recommend real world levels of artillery if you continue this. So 1 thumper tube per company, one lance/battery per 4 company battalion. Otherwise you devolve into 100% artillery and bombers.
Edit: for a starting point when designing units, the tech B abrams accelerates 0-20mph in 7 seconds. This barely is enough to displace 2 hexes in 10 seconds. So the abrams, a fast tank with its turbine, goes 2/3 with the poor performance quirk. It eventually goes pretty fast with Sprint plus road plus gps, not counting unit or pilot skills for extra speed. But yeah, a fast tech B tank is 2/3 poor performance. The rumored t14 which hasnt actually hit real production is 10+ tons lighter with the ability to supercharge its engine at the cost of greatly reduced longevity. So a techC tank that doesn't actually exist yet in production can barely hit 3/5 speed by being able to displace 3 hexes max in 10 seconds. Some cutting edge apcs/ifv exist now that can hit 3/5, again with the poor performance quirk as always. So try and avoid super fast accelerating tanks if you are near future analog, tanks that want to shoot arnt ripping at 50mph off road and take a long time to get to that speed if even possible.
