Well, it looks like it has one those video chips that are harder to mod to RGB, so sad. xD
I wonder if it's possible to "revert" it to NTSC, I don't really like it being a PAL-M unit, this standard is known for having low fidelity with colors... Most TVs nowadays work with anything you throw at them anyways.
Or maybe I should just buy a new motherboard (NTSC-U), with an easier to mod video chip? Hmmm...
Such amazing stuff, Acrof! Really interesting. The nearest I ever got to having 'exotic' Nintendo stuff was that I had a Hong Kong version of Ocarina of Time, fully-boxed. Got rid of it though, since I wanted the gold cartridge. As for your lamenting PAL - I wouldn't worry about it. I've heard that the colours are better on PAL and vice-versa. I think the truth is that, with most stuff - PAL is just better, higher resolution, and better colour reproduction (to the point where movie directors used to refer to NTSC as "Never The Same Colour"). About the only 'disadvantage' it had was it's frequency of 50Hz vs 60Hz.. but what you have is referred to as 'PAL60' over here (I'm from England). PAL colours, NTSC refresh frequency and resolution.
But with a lot of retro games, the extra resolution of PAL was not utilized, as they already optimized their engine as much as they could for NTSC. Rendering those extra hundred lines of pixels was often out of the question, especially if they wanted to keep the speed up. Many games were even slower with
borders. Rareware were amazing on the N64 with their PAL conversions. Nintendo were initially total crap, but started getting better (PAL Mario 64 has big borders and is slow, Zelda has no borders, but is slow etc). Thus, many PAL games up to (and not including) the start of the HD era were shadows of their NTSC selves. The further you go back, the worse it gets. I've never personally-seen a PAL-optimized game from the 8-bit era, and have only noticed a few from the 16-bit era which are speed-corrected (but none that are full-screen).
As for whether to get a new motherboard for your console - don't bother. If you're going to do that, then just buy an NTSC console. I have two myself (one American launch N64, and one Japanese gold edition), and I reside in good old PAL50 land! If I can get an NTSC N64 - you definitely can. That way you don't have to defile your lovely Brazilian console. A regular NTSC N64 of no particular rarity/merit, unboxed, shouldn't cost you a great deal. But why bother? Your console already runs American games, yes? I dare say you would notice no tangible difference between PAL60 (or 'PAL-M' as you call it) and NTSC. Both the same resolution (525 lines), same refresh rate. PAL60 just has 'better' colours, but I'm sure the difference would be null on a modern television.
I'm pretty sure what happened with your N64 is that it was not made
in Brazil, but merely assembled there by Gradiente so that they could apply their own stickers and various other signage on the console and included documentation. They're probably just regular NTSC machines at heart, thus running American games. I wonder, would your actual Brazilian cartridges work in my NTSC consoles? I bet they would.
When the Dreamcast launched in Europe, is was the first console to get around the PAL 'barrier' (borders, 17% slower) via a 60Hz mode built into the PAL console. This mode was actually 'PAL60', and not NTSC. The PAL PS2 included a similar mode, but this was actually NTSC and not PAL60. This is why hardly any PAL PS2 games have the 60Hz feature, as it meant any FMVs had to be stored twice on the disc, as the colour-encoding for PAL and NTSC is a primary difference. By going with PAL60 instead of NTSC, there were not many Dreamcast games that didn't offer a 60Hz mode.