ROFL, Henry did EXACTLY the same!!! Hubby was amazed at the craziness ds would get up to prior to feeding. Henry was feeding about 10 minutes in total every 4 hours at 8 weeks and gaining plenty of weight. As long as he is gaining, don't worry. Also, it sounds like he is making sure that he gets enough in the day, which might be why he is giving you long stretches to sleep in the night time. Is he still having plenty of wet and dirty nappies? That is a good way of also ensuring that he is getting enough.
Many - if not ALL - women would tell you that mostly sleep begets sleep, and if he was sleeping too little in the day time, he would rather have night wakings than sleep so well.
When he wakes in the daytime after his short naps, is he cranky/grumpy or is he full of beans and playful? (difficult to tell probably with a 8 week old, right?)
Is he properly awake? Or does he seem dazed and confused? If he is awake in the day and alert, that at least rules out an infection which might be making him drowsy at night to sleep so long.
He is generally on a 3hr EASY during the day, has a fussy session from about 5-7pm which can involve a few top up feeds.
That sounds like he is cluster feeding, which probably is contributing to him sleeping well and long stretches at night. He is ensuring that he is getting his required calories, which sees him through the night.
Sounds like you are doing well!!
I never exactly knew when all the growth spurts were, but I recall my hubby always laughing at me as i almost every second day said I think he was having a growth spurt!!

AS long as he is happy, pooh-ing and p-ing and sleeping, you are doing GREAT IMHO.
HTH
DI