Hey I'm new around the mkii section, I usually hang around with the mkiii crowd. But I find myself drawn to the idea of a mkii because of the greatly reduced curb weight.

Anyway my question is can you bolt the 24 valve 7MGE heads on the 5MGE? I like NA engines so 24 valves should flow better.

Good question on that one but I wish I can answer it. I also own a 85' supra and I would recommend you to get the 6MGE. I've never seen a 7MGE head bolt on to a 5MGE block and see how it runs with the different compressions.
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Why so opposed to the 7M block?

I theory you can get higher rpms out of the shorter stroke, but that's at the cost of the torque that the greater displacement yields. I'm not really opposed to the 7M so much as it seems like a nifty idea. Just dropping in a 7M-GE is probably a lot simpler, or better still the imfamous 7M-GTE swap. I'm just thinking of things to do when I get money.

Up to 500 bucks

The head will fit directly onto the block just fine. You'll almost certainly need to switch the 5M pistons out for the 7M ones though. 5M pistons (at least the performance pack ones) have a big dome vs the flat 7MGE ones. The other problem you will run into is that the there is no provision to mount the PS pump on the head for the 7MGE. You could mount all the 7M accesories in place, but the 7M crank pulley won't fit on the 5M crank. You are much better off just sticking the 7MGE in entirely. Displacment is king, both engine run out of power at 6K. You can run the 7M off the 5M electronics if you want. However, the best way is to run with the 7M electronics complete. Note that if you do this the wiring is the same as if you do a 7MGTE swap. In the end just stick a 7MGTE in, much more potential. Trust me I spent a ton of money on NA power only to be replacing a motor which cost nearly 3 times the cost of the car for a 7MGTE.