5 weeks - surely not enough time to recover from last week and prepare for this one? Won't it rob you of your speed heading into racing season? This might be the last time I comment here because I really can't bear to watch....
MMU is a selection race for the World Trail champs... I guess it only makes sense to do it if you want to take a punt at being selected... and if it fits into your overall plan (which seems to have been meticulously thought out).
So, Ian Bailey who won the Maurice Mullins 50k in 2017 went on to finish 70th in the World Trail Champs in Italy that year, 1 hour behind the winner.
I just think choices have to be made - Ultra / Track / Orienteering. I don't think they go together (says someone who failed to juggle track and orienteering for several years).
Would have to say I would be a bit torn between both arguments here if this was me.
My general instinct would be 5 weeks is definitely not enough to recover from the 50k in time for Maurice Mullins, certainly not to race at your best. Most likely it would go fine and Josh would make it to Maurice Mullins start-line ready to go, but it would certainly be risky to plough on and try get ready for it with the right lead up sessions etc.
I also understand it's not easy to get Irish running vests, and running would be very tempting, certainly considering after donadea, Josh must be in a very good position to get top 3 or close at this stage at Maurice Mullins.
But if you're going to go for MM, I think the whole lead up would need to err on the side of caution.
Eoin is probably right about juggling the different sports. I think you can jump between them a little - Josh using an ultra to get a good winter base will probably put him in perfect shape to lead into an orienteering season, especially as he still as time to do shorter work now if he wanted (not that he ever neglected speedwork). But it is probably not possible (or at east much harder), to be in peak shape for two simultaneously e.g. running world trail champs (44km?) on 8th June, and hoping to have a track season at the same time (May - July).
Tough decisions alright, good luck with it Josh!