Can anyone recommend any yaoi where the uke is scary looking and muscular but is actually ...

I recommend Rational Pervert Romance for the first type!! He's buff but in my eyes still a cutie bc he's such a cinnamon roll
http://www.mangago.zone/read-manga/rational_pervert_romance/

If you want a stoic beefy uke this is your guy: http://www.mangago.zone/read-manga/naked_sword_and_tree_peony_of_black/

You can also browse this list for more couples opposite the normal tropes: http://www.mangago.zone/home/mangalist/1001835/

http://www.mangago.zone/read-manga/you_re_my_princess/

http://www.mangago.zone/read-manga/nirameba_koi/

http://www.mangago.zone/read-manga/oko_sama_star/

http://www.mangago.zone/read-manga/shitteru_yo/ not muscular tho but hes cute hehe

I like this a lot
(big but insecure uke)
http://www.mangago.zone/read-manga/risou_no_koibito/
it doesnt fit exactly... uke was a lil cutie, but he had a 'Growth Spurt' so compared to his former self he is big (but he is still cute) start page 130
http://www.mangago.zone/read-manga/katsubou_no_manazashi/tr/75675/page/130/