Upgrade for 12R engine

[Dropbear]

Hey guys
In my younger days i had a Daihatsu F20 with a fiberglass jeep body on it similar to this

Which I sold a number of years ago it has since been onsold and come back to haunt me so to speak. The 12R engine I in it is getting rather tired and I have been requested to rebuild it.
However the current owner would like more power from the little beast so my question is, are there any "direct" replacement larger capacity engines that will match up with the bellhousing & engine mounts? Or on the other hand any performance upgrades for the 12R?
Any and all input will be greatly appreciated
Thanks in advance
Dropbear

[briney]

dellow makes an adaptor ring to take an 18r. i think other r motors may fit this ring too. the bit i've had to do with 12rs they need all the help they can get.

[crowncustom]

Good engine in there time but no go for todays use.Best replacement engine would be an 18R or RG or 22R-E.If the gearbox has a detatchable bellhousing then an 18R one should fit.Mid bath sump a few plates mounted on the existing engine mounts to place this back and bobs ya uncle.
Cheers Brett.

[Dropbear]

Thanks for the input guys, I'll pass the info on and see which way they want to go.