Alright well first off I'm new to this forum and I have a few questions on first my amp,replacing tubes,and things of that sort

Lets start off since I was 17 I got a Kustom 36' coupe and, with a pedal it has got the job done but I have moved on to play something more progressive that needs more than just a distortion pedal and I'm looking on tweaking the tone so I'm looking on purchasing a "Maxon ROD880 Real Tube Overdrive Guitar Effects Pedal" I heard it has unrivaled versatility (Which is what I need with such a low gain amp) and I heard it also is geared more towards heavier music which is what I'm looking for.I would like the most professional sound I can get on my little budget lol

Second question would replacing my Kustom's pre amp 12AX7 with a higher gain and better quality one.Would it help with my gain all around or worsen the clarity? I'm willing to spend anywhere to about the 70-100 dollar ball park on a tube if it is absolutely nessicary.

Third question the amp has 6L6 (x2) and I heard you can use 5881's in that socket because its a 6l6 to gov. standards(don't know if that's true) but would that help my amps tone at all or should I just find really nice 6L6's suggestions?

Also let it be known I had a guy frankenstein my Kustom on top of my laney 4x12 so its running out of that with G12T-75's

If anyone can give me some advice on how to turn this well mannered machine its highest gain potential please let me know thank you