I set out with similar objectives when building my TR7 engine nearly 10 years ago. I'd built several T140 engines previously but not since the early '80s, so I was very out of touch with where to get parts from and what had changed since the 1976/'77'78 Bonnies I used to work on. One major change Triumph made was to fit a much stronger timing side crankshaft bearing (NUP306). This is a must, in my opinion. Otherwise, the importance of getting everything spot-on during the engine build can't be over-emphasised. Thorough sludge trap cleaning (done with care to avoid making any new punch marks in the crank web); avoiding getting big end journals reground unless genuinely necessary, and then making certain that whoever does it grinds the correct .080" radius each side; valves & guides - avoid the usual items which aren't usually very good (they often come with clearances that are way too large) and invest in Hidural 5 / Colsibro guides (Norman Hyde sells good ones) and G&S valves, with the guides honed to the optimum clearance after fitting. JCC (aka Wassell) pistons are good but unless things have changed, the rings they come with aren't the best. Goetze rings are, as far as I know, the best available in UK.
Compression ratio - there are three piston types, 8.6:1, 7.9:1 and 7.4:1. I have 8.6:1 in my engine and they're fine, though 7.9:1 would probably be good,and more tolerant of high ethanol content petrol. A good cam combination is the standard inlet cam with 70-9989 exhaust cam. These are easily available and good quality, and a fair bit cheaper than Hyde's.
Care should be taken to verify that main bearings are made in UK, Germany, Japan, not Far-Eastern items. RHP / SKF are good.
Proper attention to every detail, eg: checking and flattening mating surfaces etc. Copper head gaskets are better, in my opinion, than the composite type, which need repeated re-torquing. Good quality gaskets throughout are important - worth spending a bit more if you can find better quality than the usual offerings, which can be made of material which splits easily and / or with holes that don't align perfectly.
I'm sure others will give plenty more suggestions (and probably criticise mine), but I hope this is of some use.