Gill:

Talk about going off the deep end. Pusher, engines on pedestals, and a bash to boot. I don't think anyone has done anything similar, probably why you've gotten no response.

I'll dive into the deep end with you, giving my thoughts with no guarantees at all.

Basically, it should work.

I would not use any down thrust with the engines up in the air, if anything I'd have them angled up. Consider the effective thrust, if it's down it will tend to make the plane nose down more, while the up thrust would decrease this somewhat.

You will without question need vertical fins/rudders if one engine quits, with both running rudders will also help if they aren't quite at the same rpm. Recommended highly.

Side thrust? Your choice. I build all my twins zero side and zero up/down, the enforcer though, with the minimal yaw control of the delta I might well put some side thrust in.

How much up/side thrust, how much rudder/vertical fin? I'd be inclined to make the engine mounting adjustable, and make the fin/rudder set as big as I could without just looking wrong.

But whatever else, keep us informed of your progress.

Bill.