tubular manifolds, nt all tubular manifolds are the same, i found the ABF prefers a Tri Y compared to a 4-1. get the lengths right on a tri Y and it'll gain some good torques
throttel body, bigger hole allways helps.
chips can help give a littel extra, they are cheep about £1.81 ea for a blank eeprom if you cant be arsed tweeking it yourself you can ether copy an existing chip that is known to work well or try various downloaded ones, ( some are good some are sh!te)
now thats the easy bits out the way now you need to go shopping.
silverline pencil air die grinder ( its the sae as the sealy one biy cheeper ) some cheep tungsten carbibe cross cut burrs, sanding bands and manderls 6 and 13mm and somem flap wheels. borrow a mates air compressor, the whip the head off and strip it.
spend the next 8 - 12 hours in the ports and chambers optomiseing them, you dont need to take out LOADS of metal just smooth the shape and loose that bloody bump on the short side radius, then de shroud the valve seats into the chamber. next come the valves and seats it's possible to blend the seats with a grinding stone on the die grinder but thats a lot of effort and easy to mess up. id suggest haveing a machene shop tri cut the seats and whilst your at it have the valves 3 angel ground.
done well that lot should have given you your 25bhp and can be done for less than £200
next come the cams. as three_ess found the shrick 266 ca,s fitted as a pair loose mid range torque but the shrick 266 inlet cam with the stck exhasut cam makes nearly as much power but with much better torques. problem is shrick cams are expensive the good news is that cams can be reground

the std hydralic tappets have enough adjustemt in them to allow as much duration as a std bottom end would take. regrinding to 272 is possible, the massive bounus is you can pick and chooes what profiles you want. 272 inlet 266 exhaust has been tryed and liked but 266 inlet with std exhaust works well, cams can be reground for less than £100 a stick
thats clean over 175 bhp