if you want adjustable followers i think you need to strip the block back to bare bones as the block needs a hole drilled where the followers sit (or so i have read) if you want cheap and easy oomph then i would suggest the following:-
1) port and polish the head and block around the valves (just slight relief not full flow or it gets pricey... you can do this yourself with a die grinder and stone mandrels)
2) change out the cast exhaust manifolds for stainless ones (with better flow) OR port the cast ones out with a die grinder to match the exhaust ports on the block
3) centre main strap (stops blowing out the centre main when you over rev)
4) change the carb.
should point out that none of the above should even be attempted until you know the port velocity limits etc for the unit ! otherwise you take too much out and jigger the engine.
when you get into the realms of adjustable followers and cams it gets pricey you then need to consider high flow oil pumps etc etc... then its a case of why stop here i might aswell lighten cross drill and balance the crank and rods, and pop a lightened flywheel on whilst i am there.... KACHIIIIING !
if you want more CR then simply facing the head and deck will achieve this.. now remember when the CR goes up the quality of fuel or octane should go up too otherwise you blow holes in pistons.
from my own meager experiences in a carrier i have driven 60hp and 85hp units.... even the lowly 60hp unit was more than enough ! and the 85hp unit was very good more than enough to do what you need. so if you get a 24 stud 99a (100hp) you will have more than required...
i am afraid I have the "BHP" T shirt i spent just sickening money getting a 1300cc mini engine to exceed 200 BHP.... i got there in the end but my was it costly
and finally whilst i ramble on... you need to consider the tollerences of the running gear.. will it take greater BHP and torque... and if so how much ? i have seen diffs stripped clean of teeth and they never go quietly something always gets taken out at the same time...