Ok you have a few issues here and getting the old bush out is one of them .
Alloy castings will need very carefull heating if they are in any way delicate as alluminium will lose a lot of its strength if heated too much .
If possible i would try to grip the flange of the bush and see if it can be turned .
If so try twisting and pulling .
If not then i would try filing a groove through from the inside using a triangle shaped file then try to crush the bush in so it releases- being carefull not to cut into the housing with the file of course !
I would use heat as a last resort as it is difficult to control and alluminium will not show how hot it is until it melts – you can blacken it with the soot from an oxy acetylene torch and this will burn of just before it melts but knowing how much weaker the casting is at that temperature is a lottery and what aboult distortion ?
You could use a large soldering iron to apply some heat on smaller items and this will weaken any loctite that may have been applied to the old bushes .
Another way is to heat up a suitable piece of steel until it a drop of water will skitter across the surface then sit the item on it until it is too hot too touch comfortably as the alluminium will suck up the heat very quickly – obviously if the item is large this will not be practcal .
I take it that you do not have a lathe to make the new bushes yourself ?
Once you have these made- with the bore undersized (.001-0.003 inch ) you will have to push them into the housing and ream them otherwise both bushes will not be aligned to each other and the forces applied to the bushing by the housing will more than likely squash it a little or knock it out of round so the throttle rod will not fit .
As for the press fit it wil depend on what temperatures this item will have to endure as the coefficient of linear expansion of alluminium and its alloys is different to that of bronze but i would suspect .02mm or .001 inch would suffice and you can use loctite etc .
If the bushings are thick enough you could possibly bore/drill them out oversize and push and loctitein a new liner then ream as above – maybe easier .
Ian