Between the aluminum plates, you could machine a groove for roll rubber “o-ring” material.
Where they butt together, a small dab of silicone or adhesive.

This way, you can always take it apart without having to damage the mating surfaces.
Might want to make a couple of pockets for your screwdriver to separate the two plates in future too.
Perhaps in not so visible location to take away from your art work.

'Right Stuff'......is it better than blue RTV. ? (or a better advertising campaign !?) Jus ax'en
6sally6

With a small groove, it should work great. Will there be gas going through the intake, or just air?  If gas, I would be concerned.

Nos681 wrote:

This is an example of material I am referring to.
They are available in oil/gas resistant types and diameters.

https://www.zoro.com/zoro-select-rubber-cord-buna-116-in-dia-10ft-zusa-rc-475/i/G7628162/

I have made a lot of o rings out of similar material and never had a failure. To make the seal, I cut the ends of the material on a diagonal (opposite diagonals on each end), overlap the diagonally cut ends, add the right stuff, and you have a seal. The operating pressures for my application ranged from 35 to 65 psi.

I've made some experiments using my 3D printer and made a couple of gaskets using ThermoPlastic Polyurethane filament.

Nos681 wrote:

This is an example of material I am referring to.
They are available in oil/gas resistant types and diameters.

https://www.zoro.com/zoro-select-rubber-cord-buna-116-in-dia-10ft-zusa-rc-475/i/G7628162/

That is the stuff I use to seal the lower units of the old 50's Johnson outboards I restore, in 1/8" dia.  Works great.

Ron68 wrote:

That is the stuff I use to seal the lower units of the old 50's Johnson outboards I restore, in 1/8" dia.  Works great.

how do you prep the surface? are you cutting groove? what do you do where the ends meet?

Daze wrote:

Ron68 wrote:

That is the stuff I use to seal the lower units of the old 50's Johnson outboards I restore, in 1/8" dia.  Works great.

how do you prep the surface? are you cutting groove? what do you do where the ends meet?

The lower half of the lower unit has a groove cut in it that ends on either side where the bearing housing for the output shaft rests. I cut the cord about 1/8" long at the ends. The upper half of the lower unit is flat and when the lower half is bolted on, the groove (about 3/32" wide and 1/16" deep allows the cord to expand and fill the groove. I hold the cord in place with some Permatex #3 liquid gasket sealant. FYI - here is a link to a parts manual for a 1956 10 hp Johnson. Page 16 shows the seal (20) and the lower unit assy. You can see how it is installed in the groove.
Link: https://www.aomci.org/wp-content/uploads/attachments/Johnson%20QD-17%2010%20HP%201956%20Parts%20Manual.pdf
 

If RTV does the job where the ends of that seal meet, why not just use it for the entire seal. The beauty of RTV is you install it wet and then it doesn’t spend the next twenty years trying to squeeze out of the compressed area it is in.

MS wrote:

If RTV does the job where the ends of that seal meet, why not just use it for the entire seal. The beauty of RTV is you install it wet and then it doesn’t spend the next twenty years trying to squeeze out of the compressed area it is in.

To me it would depend on how often you would need to take it apart.  If the answer is basically never, then no reason not to use RTV.  If its something you may need to remove semi-frequently cleaning up the RTV is a mess.  Using RTV for an oil pan, intake to the block, etc. makes sense; those should never need to come apart.  If it was say upper to lower intake on a 5.0 I wouldn't use it because there are times when servicing certain parts of the engine are at least easier after removing the upper. 
 

MS wrote:

I do not understand the part about hard to clean up. I have never had any problems using single swipe with a sharp wood chisel to clean the stuff off. And on intakes and pans, a cup wire brush on my hand grinder makes it super clean really quick. And, Ford sells a RTV remover spay that works super to dissolve it.
But, my main thought is that I want the best stuff to put something together with, not the easiest to take it apart. I put stuff together with the intent that it will stay together. If something has to come apart, I will deal with that at the time.
I understand some parts like upper intakes need to get removed occasionally, but I just use a good FelPro gasket for stuff like that, with no sealer on it. Same as a carb gasket.

I have to say that I'm also a little confused regarding cleaning up RTV as I've also never had any issues removing.  I typically use a razor scrapper where I can't rub it off with my finger.  
 

Okay, I see the issue, you are translating a pain to clean up as "hard to remove".  Its not hard to remove; its a pain to clean up.  Given the choice I'd rather not have to clean it up.  I'd always rather have a reusable gasket provided sealing is equal.  This is why I don't use RTV on rears anymore when a LubeLocker is available.  I've never had a problem getting RTV off.  Soak it in the parts washer overnight and it usually mostly falls off.