For me, it has been very easy and well-received to tell them what's on my heart when we are drunk. If any of you has insecurities with male-friendly affection (bromance), specifically mention that your feelings aren't romantic. I think they will understand what you mean because they probably feel the same.
When I was young, my brother and I were basically the worst enemies. Fighting, hating, ignoring each other, mocking, insulting... you name it! Then when we left the family house, all of this calmed down.
After some years, one day we finally met randomly at a bar when both were a bit drunk. A lot of buried feelings came out and we had a heartwarming moment of reconciliation, excuses and forgiveness and mutual understanding. Since then we are a lot more friendly with each other and don't have a problem with each other anymore.
About friends. I have a big group of friends that became very important to me at one point in my life, and I told them a few times how important and cool they were for me, while being sober. We were eating all together at a big table and I made a kind of "I have an announcement" moment. I said something like:
Guys, you really are an amazing gang and I'm very happy to have you in my life.
It was a bit embarrassing, a bit "cliché", a bit funny, but definitely it was positive for everyone. They might not start a discussion about it and brush it off immediately, but they will understand what you said.
On a more private, one-on-one basis, for some friends it happened when they were very drunk and spilled the beans:
I ******* love you man, you are awesome.
You are a really cool friend.
And things like this.
A lot of it comes from trivializing the word "love", showing that you are not shy to use it in a friendship way: sharing love, spreading love, showing love.
Physical contact like hugs are also good. If you never had hugs and love-sharing with your male friends, don't rush at them with 110% affection, start with a little bit, high-fives are more comfortable than hugs at the beginning. Normalize friendly love and affection, if it feels not normal for them.
Don't express too much: to repeat I love you 6 times to your male friend might bore them. Guys will understand when it's clearly explained once. Girls might like to expand, talk and discuss a lot about your reciprocal feelings and blabla.. guys will not want to complicate like this. Make a simple, fair, understandable statement, like "I love you man", and the other guy will express the reciprocity. After this, it's better to leave it at that, avoid misunderstandings.
"I love you" is also very general. There are probably more particular things you can say to different friends, here are some examples:
"It really makes my day to spend lunch with you"
"Working with you is great"
"You are very interesting to talk with"/"You are a great listener, I feel like I can open-up with you"
"It's so damn cool to FINALLY meet someone that likes the same movies as me !!!!!"