Prop- tried a few times last week to reply to this but my Workstation kept throwing me out!
I too am a “Big unit” and have through trial and error come up with a few ideas on this that have enable me to avoid injury whilt boosting endurance etc. Here goes:-
1) Jogs/ Long runs- no more than 20 mins and only on grass. You can do them daily if you want.
2) Good trainers- I use Brookes Beast which are specially designed to give cushioning/ support/ control to the big lads!- I have had 3 pairs on the trot and will not run in anothe rpair of trainers ever!
3) Join a boxing gym. The bag work/ sparring/ calisthenics will strip weight off like you wouldn’t believe and the skipping will improve your agility no end.
4) Look at the demands of your game-an Ru Prop- wrestle/ maul/ ruck/ scrummage followed by short sprint repeat. Try and mimic it in some way.
5) High rep weight lifting- BB/ DB/ KB whatever gig compound movements for high reps. Ash’s Beastly combo’s are just the job.
6) Track work- nothing over 400m and if you get spikes make sure they are distance spikes with a decent heel in them.
Hope this of Help.