I’d highly recommend something with a pneumatic shot. I’ve owned lever operated bench top machines and it’s just incredibly frustrating to get consistent output, especially as the shot size increases.
Your options are largely going to be based on budget. Maybe check out beagle buster, it’s got a decent community, the price is alright, and it’s been around long enough to be proven out.
Here’s a fairly long thread that covers various topics, might be worth a read: Benchtop injection molds on nomad - #33
And I’ll try to dig out some private messages with good info that spun off of that thread.
The biggest issue I see you running into is probably clamping force. Nobody expects clamping to be the problem but as your cross section increases, the force pushing your mold apart increases proportionally (and your enclosure has a lot of cross section 
)
Anywho, I figure I’ve got more experience than most in this arena so if you’ve got specific questions, feel free to ask. Maybe we’ll end up with another nice compendium of knowledge for this weird niche use case