Kia FE3 Interchangable Trans?

I've driven on the highway for a while with 15x8 rims with tiny tires and have lost quite a bit of top end. At 3500rpms i do about 70.. I understand some have swapped their 5th gear with an RX-7 5th gear for some top end.

BUT.. I was thinking, if an FE3 engine bolts up to B2's trans. Could an FE3 trans bolt up to the B2's engine for more top end? (Idk if there'a a 6th gear involved) Or perhaps the FE3 gears are swappable with B2's gears? Understandable if some linkage would have to be modified or fabricated, just want to know if it would be possible?

I think the rx-7 is the first thing you should address. However if you have any fab skills once the trans is on the ground in front of you, and if you did already have the kia trans, you could make the mount by adding material to the mazda and lining up or the kia, or some of both. You probably also will have to address new output shaft compatibilities and driveshaft lengths.

I dont know the final drive and the 5th gear of the kia. if might not be much different from the b2200 because as a small suv it's got small truck tires too as far as circumference.

I have a 91 RX7 non turbo 5th gear (along with the rest of the RX7 drivetrain), and with 15" rims and 205/70R15 tires, I am running just over 2000RPM at 60MPH. I have a stock B2200 rear axle ratio, if you swap in the same 5th gear you will have the same RPM's. Its about a 1000RPM difference between 4th and 5th at 60MPH. I believe the 5th gear ratio I have is 0.69:1, which is a lot different than the 0.89:1 that the B2200's have stock.

195/50/15's. First gear isn't much of anything anymore haha. Can accelerate easier though.