Personally, I find squeezing thickened epoxy out of a disposable pastry bag or a freezer bag gives much better control than a caulk gun.  You can feel the pressure in your hand and it won't keep flowing after you stop squeezing unlike every caulk gun I've ever used.

FYI - I do not have first hand experience with this. I cannot imagine any catastrophic reactions. Both products are made from epoxy and hardener. In response to Pete, the caulking gun is being used because the West 10 is a new product which could really speed up the filleting or epoxy tabbing process. It comes in a tube for a caulking gun and has a special tip on it that mixes the two parts of epoxy. The result is a nice product that saves time and has little mess. Personally I have used thickened epoxy with silica and wood flour. I did the epoxy tabbing and filleting after taking the copper wires/"stitches" out. This was time consuming and I would definately consider the West 10 for the tabbing process that Dave wants to try here.

Although I agree with Pete on the pastry bag (I used zip-locks with a corner cut off) I can see the appeal for the West 10 and think it should work fine though I would be careful on the cost.  Also, from my expereince with these types of products they are a one time use, so once you have cracked it open, you are committed to using the entire tube.  There is a version of this my blacksmith uses for hoof repair (yes horse hoof) that has two tubes in a special caulk gun and has multiple tips per tube so you can dispense only what you need.  Looking at the West system website, it looks like a single use tube.

Now back to your original question: will MAS "react" with the West System.  if you are mixing them uncured, not a good idea, once they have cured should be fine.  Give the pastry bag method a try, I find it far easier than working with a caulking gun, to each his own.

just re-reading Danno's posting, I too did the tack-welds and remove the stitches and was surprised how quickly the process went.  Also keep in mind the only real time savings is stiring the epoxy.  There might be a slight differnece in dispense time, but again, I found the pastry bag method surprisingly quick.  The rest would all be the same regardless of method.

I am interested to hear Dave's results.

My $0.02

There are a couple of ways you can use two different epoxies and not get into trouble. First of all, you can run the fillet and let the epoxy set to slightly firm and then do your other epoxy/glass right on top. If you let it cure more than 24 hours you might have to sand before the glass work, so only let it set firm enough that is doesn't move around when applying glass/epoxy on top.

Secondly, you can run your fillets and then apply peel ply, let it cure and then rip the peel ply off as you start your glass work. I prefer this method when doing a fillet that will be visible as you can smooth the fillet to perfection, and when  you rip off the peel ply, you'll have a perfectly contoured surface on which to lay your fiberglass.