I’m 160 and 5’7″ and ran Masters at 405 for many years, so I have a similar problem as you do. Add in the extra 12 lbs of weight on rear tires (405 vs 365), my short height, low weight and low grip Mojo tires and it becomes very difficult to flex chassis.
I’ve had 3 brands of chassis over a period of 14 years of relatively heavy duty karting. Started out on a 32/32 mm (not OTK) kart, it was always pushing. I then went to same brand with 30 mm main rails & 32 mm cross rails, it was better but it was fast only for 2 -4 laps. After that the rears would get hot and greasy from the sliding and the lap time would start to fade. I think this was due to the IR not lifting enough.
Went to OTK 30mm/30mm and it was consistently faster and rarely pushed. I’ve never tried another 30/30 chassis but there are other newer 30/30 chassis (2014, 2015) that could be as good as an OTK.
After running OTK for 3 or 4 years, I switched to a 3rd brand 30/32 chassis and I had the same problem as the first brand in 30/32. I then switched back to OTK 30/30 and I was instantly faster.
All that said, If you can’t get a good 30/30 Tonykart I suspect that a another brand in 30/32 would work, especially if you plan to run MG tires (not Mojos).
I just wanted to add, that the good drivers can make most chassis work but if you’re an average racer, which is me, I couldn’t recommend anything other than an OTK chassis.