Is there a difference between the flange inlets on risers between say Mercruiser, GIL and EMI?

The outlet on the EMI Thunder exhaust is rectangular which looks to fit the factory mercruiser risers (cast) but all the SS Risers are round. Do the EMI Risers look different on the underside (inlet) of the flange / riser?

I've posted a pic of my riser base and the outlet on my exhaust. They don't line up but are the EMI risers any better?
Thanks in advance!

You have to use the same manufacturer's riser with the same manufacturer's manifolds. The only exception I know of is Gil risers can be used with a certain Hardin Marine header.

I think merc and GIL are the same !!!??? But don't beat me to it .

Thanks for that,
If I was to make an adaptor flange / spacer that channels the exhaust better, do you think that would work or might it cause some problem I haven't thought of yet?
Cheers!

Mercs are made by Gil and stamped with the mercruiser logo.

Yeah John now i see what you were talking about.An adapter would need to be crafted.Drill out the riser holes slightly.Block the slotted water in the manifold top with the adapter and a smooth transition from the rect outlet to the round riser inlet.A 1 " aluminium block should do it.Hows the height?

Morning mate,
Height's fine, I've got about 2"-3" to play with under the hatch before it fouls. I've made a mock up adaptor out of MBF by screwing 3 bits together, drilling, cutting then filing smooth. Doesn't look too bad and it does block the jacket passages.
Hell, adding 1" might even help to counter this 'reversion' phenomenon we've heard so much about!!
I'll need new exhaust hose now though!
It's always something!
Where's the pics of yours???

Keep the idle up and reversion won't be a problem.If you do get reversion i've found a nice simple fix.Big supercharger on top,blows everything right out.

NICE!
So does that mean you're going to supercharge the Skater now?