Are we doing this right?

cool. I know a guy that put the driveline from a Ford T-bird turbo coupe in one. Rebuild the quadrobog and roll.

We have two SUs but they're too small and probably worth more to ebay them anyway. Also I couldn't pass up the quadrabog when I saw it, seems too perfect for Lemons.

The moss kit would have originally come with an SU H6 carb (i.e. 1 3/4).  Seems like a quadrajet would massively overcarb that setup plus require a fair bit of work to adapt.  That Stromberg appears to be a 175 but the problem with that one is that it's a later one without an adjustable jet or many options in needle jets.  You can always sand down those jets however.

Stock 80 MGB would be a strong IOE contender at any race.  As someone who has 6 or 7 IOE patches on their uniform the main thing I can stress is that you have to make laps.  A lot of them, like finish at or near the top half of the field.  An MGB with a kludged blower that makes 20 laps is at best an Org Choice contender.  I get the enthusiasm but it seems like the window for winning an IOE is generally only a handful of races.  IMHO if it takes you more than, I'd guess at most, 3 races to get that kludge to run long enough to get near the top half then the ship has sailed for winning IOE.  Granted every once in a while they give it to a pile that keeps showing up and not winning IOE but even then it needs to run a lot of laps.  The guy offering you the free SUs is a great example.  Wouldn't you think a diesel Porsche 924 should be an easy shoo-in for IOE just by showing up?  Not so much.  Gotta run laps.   If you are serious about IOE as a goal, I suggest either running the MGB unblown or go with what has proven with that setup which is an SU and run it pig rich so you don't burn it down.

It depends on whether or not a Gaz Volga or a Moskovitch shows up at the same race, but top half for a MGB with or without a blower puts you in a "It's yours to lose" category in my book.

I'd say a fair shot, although a lot would depend on what else was running at that race.

There's a significant amount of capriciousness in deciding these awards, but a somewhat consistent factor is a sliding scale of expectations. If you bring something that makes the judges and organizers seriously question your fundamental grasp of objective reality, then it just needs to turn laps for most of the weekend to be in contention. The laps don't necessarily need to be fast enough to accumulate into a high-placing finish. If, on the other hand, you bring something that's a poor choice for endurance road racing but not staggeringly, wilfully inappropriate, then it had better not only turn laps all weekend but do so at a fast enough rate to finish correspondingly higher in the standings. Nothing's guaranteed, though. In this case, the fact that Moss makes a similar kit for MGBs and that regular, non-insane MBG owners (to the extent that this is a thing) install them of their own free will, suggests that this setup would be closer to the "poor choice" end of the spectrum than the "probably beyond the reach of professional counseling" end of the spectrum.

I guess the short version is that if I were to set out to drive another MGB in Lemons, I'd put a BMC B-Series diesel in it.

This is the wildcard in the deck....
As a mere mortal with only 5 I.O.E.patches on my uniform,I will say that there is really no guarantee that the clapped out POS you bring won't be 'out-clapped' by something else.The trouble is,you won't know you've been outdone until race weekend rolls around and you get to see the rest of the field.....