Something that I'm looking at modifying into an actual TTRPG system is the old Grail Quest system (from the choose your own adventure gamebooks). It probably will be very encounter heavy, so not what you're looking for, but once the details are worked out it should provide a suitably humourous backdrop to add some reasonable RP mechanics into. RPG-lite, but I'm hoping the flavour will cover for the systems inadequacies. At least the combat is more "averageable" than D20 due to the mechanics. A simple skill system shouldn't be too hard to put on top of it all, without getting bogged down (I'm thinking of a three-resource system of effort that gets expended as you use them, Daring-do, Smug-glibness and Brain-hurts). Classless system, but different characters will be better at different things. The horrors of Dreamtime to "recharge" lifepoints or resources should be a fun little side effect no matter what's actually happening (or not happening) in any adventure. Nicely capped magic too, removing any hassles for the DM.
edit: Anyway, for the system, I'm pretty much decided on the physical side of things being tied directly to lifepoints, with strenuous activities essentially costing you health. This can be combat related coolness, but not necessarily. You can use the four resources for various purposes, with a roll against that resource number. Think of Luck in the old Fighting Fantasy gamebooks, except you can use more than one point to modify a roll by more if it seems to be a difficult task. But successful or not, you now have less of that resource to work with (making successful modifiers less likely, and with penalties for failed rolls). There will be a basic skillset of "things you can do", costing resources with or without modifier rolls, but it's meant to be a fairly free-form system with the DM determining difficulty and costs for some of the stupider things players come up with on the fly. Combat can be miniature/floor plan based, but isn't intended to be other than as a reference (movement isn't in squares and Daring-Do and Muscle!(LP usage) can break most bounds of that system if enough resources are used or rolls are high enough anyway). Movement speeds are descriptive rather than numerical.
As the background for adventures is the DM playing as Merlin netting people through time-travel into his quests, it makes for easy/enforced adventure hooks. The different time periods also make for an "anything can happen" system, allowing for all kinds of situations to occur. The DM is also expected to take on the role of the Poetic Fiend at least once per adventure, just for a laugh and some flattery (or easy outs, hurry-ups and mcguffins for the players).
It should be able to be played as combat heavy, RP heavy, or a mixture of both, with much determined by how a player portrays their actions rather than a huge list of skills, feats, modifiers and tables. Humour is the main key, with dice playing an important but secondary role. Character creation is being tweaked, but there will only be a few main archetypes, basically differing in resources rather than skill sets. Magic is for everyone (or no-one, depending on the adventure) and is handed out by Merlin (the DM). Everyone can do everything, but some more reliably or more often than others.
With 8 books of reference material to work with, it shouldn't be too hard to put together something fun to play.
(while you can still track down the books at op-shops and second-hand bookstores, sometimes they're a bugger to find. But, ummm, Abandonia. Just so you can get an idea of the feel of the system/gameworld. I collected most of them as a kid, but as a useful online reference, Abandonia's gamebook section. Then delete them immediately. Of course)